Did you read the particular reviews or just browse the intro info from the 3 links of his i provided?
From his 870 review:
(5 of 7 Sound-related) 7 improvements in PX-870 over previous models:
1. The piano sound is noticeably better than on the previous models because the piano sound chip was upgraded to be even more natural like a real piano with better expression and more organic piano tonal elements than before. You can really tell the difference if listening to both models. Also there is one more acoustic piano sound added along with some of the non-piano instruments that have been re-voiced and improved for greater authenticity. The stereo strings, choirs, harpsichord, electric pianos, etc, really do sound good and are a joy to play especially as compared to other digital pianos in this price range.
2. The sustain pedal decay time has dramatically improved so that when you hold down the sustain-damper pedal you will hear more sustain volume and noticeably more sustain decay time than ever before and when that happens you get a more organic & natural piano sound particularly when playing legato and using more sustain pedaling. The notes of the piano sound mix together more evenly and produce a smoother and more balanced tonal expression across the entire 88 keys that was not able to be achieved on the previous models.
3. The speaker projection system has changed on the PX-870. The former models had a hinged lid where part of the lid could be propped up so the piano sound could come out of the piano top. That was a very good idea but the down-side was that with the lid propped open, you could not rest any music, music lamp, or any other items on the piano top because they would fall off. Casio designed a new speaker projection system that allows the piano sound to come up and out of the piano top without the need of a lid.
There is a brand new speaker system in the piano that diverts part of the piano sound up and out through a long but narrow speaker grill that goes the length of the piano top and is inset and flush with the top. It's located more towards the back top of the piano. The piano sound is also projected forward through speakers in the piano.
In this way there is better sound disbursement and top remains closed so it has a sleeker look, no more hinged lid like the previous model that could potentially break, and you can put things on the piano top without those items sliding off because of the previous models' partially raised and tilted lid. These are very well designed improvements that upgrades this new model in a noticeable way.
5. The headphone listening experience has been improved over the previous models with new "headphone mode" with improved electronics that creates a more realistic stereo listening environment when using any good stereo headphones.
6. A Volume Sync system has been added to the PX-870 which allows the piano to have better low frequency response when playing the piano at lower volumes which is a good thing. This type of electronics has been available in digital pianos before but not in this price range.
PX-870 Key Action
As far as the the rest of the piano goes, and especially with the key action, Casio has kept their popular 3-sensor per key-weighted-graded piano style key action in the PX-870 which was also in the former model. I believe they're doing this because so many people who owned the prior model really liked the key weight, balance, and movement of that key action so it has not changed and 3-sensors per key helps with better key repetition recognition. When it comes to shopping for a new digital piano, the key action should be considered the most important part of the decision making process for most people including piano students. Personally I like the Casio key action better than the other furniture cabinet pianos under $1100 internet price and it feels like an acoustic piano in a number of ways.
Be aware that no digital piano in this price range actually feels exactly like a real acoustic piano, but this one comes pretty close and for most people, including more advanced players, you can take your music pretty far on this new piano. Also th new synthetic ivory and ebony key-tops have been improved and are much smoother with a better tactile feel than ever before and I noticed this right away when I played it. The synthetic ivory and ebony keys also help with absorption of moisture from your fingers so that the piano is more enjoyable to play if you're the type of person who has sweatier fingers.”
From his S3000 review ( *a particularly good read because of the section that explains how different brands’ generic support of “GM” often does not equate to consistent playback sound when playing “GM MIDI song files” through this DP versus that DP versus the other DP/drew-r):
“ PIANO KEY ACTION, SOUND, AND PEDALING
So now that I have explained how great the overall music can be in this instrument, the actual "star of the show" in the PXS3000 is the new piano key action, piano sound chip, and piano pedaling system because after-all, what most people want when purchasing a portable (or any) digital piano is for that instrument to be as realistic as possible in terms of an authentic piano playing experience within its price range. Up until now there has been some acceptable portable digital pianos and some good portable digital pianos out there under $1000...but nothing truly "hands down" outstanding. Yes, there certainly are other portable digital pianos with some compelling digital technology built in such as the Casio PX360, Kawai ES110, Roland FP30, and a few others as I mentioned earlier, but not with the capabilities of this new Casio PXS model. I do know there are people who don't want to spend any more than about $500 for a new digital piano and even Casio has a couple models under $500 that could be good options for the beginner.
But for just a little bit more, the PXS3000 is much better and you would likely want to keep this instrument for many more years than the others because of the upgraded features that enable you to do things with your music that you would not otherwise be able to do if you spent less money or got something else.
The new piano style key action in this PX-S3000 is graded and fully weighted and one of the best in its class for its price range. Also, for the first time Casio has created individual linear weighted keys that vary in weight per key as you go up and down the keyboard to give it better balance. The variations are definitely subtle and not easily felt but they are that way on real acoustic pianos as well.
This key action is definitely not a grand piano key action and is instead more of an upright piano key action as are all the other digital pianos in this price range in terms of the key movement and key balance from front to backs of keys. I did notice the white keys were fairly firm to press down towards the backs of the keys (pressing towards the front is fine) and I would have preferred them to be easier to press down, which is the way it normally is done on real acoustic upright & grand pianos when pressing towards the backs of the keys. The keys (the part you cannot see that goes under the control panel) are just a bit shorter in length on these PXS slimline portable digital pianos because of space restrictions in being so compact. Overall the keys are balanced and move nicely considering the compact nature of the cabinet and in fact is much better than I expected.
It is noticeably more stable and with less key-bounce along with being quieter in movement noise than in past models, and the upgraded synthetic ivory & ebony key-tops provide just the right amount of textured key surfaces for great tactile feel under the fingers. With the upgraded triple sensor electronics for each key which offers better key-repetition note recognition when playing faster (and/or not letting the key come all the way back up before pressing down the key again), I am very impressed overall with this new and improved key action and it certainly responds well to all types of playing and noticeably better than its current competition.
I will mention that the black keys are lighter and easier to press down than the white keys and for some reason a few people out there don't seem to like that. But for me and the majority of people I know who play piano, the lighter black keys are a good balance to the white keys in providing a quicker key action that is responsive as opposed to much heavier black keys as is the case on many other brands. You definitely do not want heavy black keys because it will throw off your playing technique in a big way, especially given the compact nature of the PX-S3000.
So in my expert opinion for its size, price range, and compact footprint, Casio did a very good job designing this new key action although I would have preferred longer keys but then the physical size of the cabinet would have had to be larger. If you are the type of person who will be playing primarily classical music then this model may not be for you with regard to a fuller, larger key action and there are other things out there to choose from.
As I said, the PX-S3000 does have slightly shorter keys (the part of the key you cannot see that goes beyond the visible key and underneath the piano panel behind the key) than some other digital pianos and therefore the key weighted movement towards the very backs of the white keys and black keys is harder (firmer) to press down when playing flats & sharps than other digital pianos and acoustic pianos. Just so you know...the actual keys themselves on digital pianos don't have much weight to them at all. It's the extra weights placed inside the key (in acoustic type piano keys) or attached to the keys or the fulcrum point location that give the plastic and/or wooden keys their complete down-weight and up-weight movement. Acoustic Grand pianos have much longer keys (the part of the key you cannot see that goes under and behind the panel into the piano cabinet) and that is why professional piano players and advanced pianists always prefer to play on grand piano key actions because they can play their music better with more balance between the backs and fronts of the keys in terms of key pressure and key stroke.
As a real life example, the down-weight of middle C# key (black key measured in the middle of the key) I have personally measured key-weight movement on some Yamaha acoustic upright/console pianos where that key down-weight is about 60 grams of down-weight pressure. The down-weight pressure or force on the same key measured in the same place (middle of key) on the Casio PX-S3000 is approx 65 grams. But if you take that same measurement on the popular Yamaha P515 portable digital Piano key length & weight in PXS3000 piano ($1499 price) the down-weight measures approx 90 grams on that same black key in the same position...this is true of the white keys as well. The Yamaha digital piano key action is noticeably heavier in that key position not only against regular acoustic upright and grand pianos, but also as compared to Korg, Kawai, and Roland digital pianos with Roland needing more key pressure than Kawai, Korg, or Casio. On a real grand piano the amount of finger pressure needed to press down the key is even less than upright acoustic pianos. In other words, the keys are even lighter and normally take less effort to press down on grand pianos as opposed to upright pianos.
To get this more portable and physically slimmer size digital piano, Casio obviously had to compromise to achieve that new reduced size in the PXS and so the keys are a bit harder to press down as you play towards the very backs of the keys because of a reduced fulcrum point. But...given the fact that (overall) the 88-keys outplay many of the other brands of portable digital pianos under $1000 when it comes to key weight and movement, I believe it's a reasonable compromise other than not having such a slim cabinet and making each key a bit longer.
That is what I would have personally preferred because that "extra slim" design is not the reason I would personally buy this model to save an inch or two in depth...it's having the best piano playing experience I could get for this price range in a portable digital piano along with all those other cool features. Nevertheless, I really do like playing on this PXS key action.
PIANO SOUND, POLYPHONY, & ACOUSTIC PIANO SIMULATOR
The new 192-note polyphony piano sound chip is dramatically improved over past models and is so good that I thought I was playing a much higher price range of digital piano and also another higher priced brand. The realism of the Casio piano sound chip has always been somewhere between acceptable and good in prior models in trying to duplicate an actual piano sound, but has always been lacking in some ways with regard to tonal resonance, sustain/decay time, and natural organic overtones and sympathetic vibrations normally found in real acoustic pianos.
In other words, the prior Casio models have been more artificial in its acoustic piano sound and with less polyphony piano processing power and this includes the other current model PX Privia series portable digital pianos that are currently available under $1000. But the new stereo grand piano sound in the PX-S3000 is really impressive in its ability to not only sound like a real acoustic grand piano (just because a digital piano doesn't have a grand piano key action doesn't mean it cannot have a grand piano sound), but to have an incredible amount of dynamic tonal range offering a huge amount of dynamic expression that I never thought would ever come out of a portable Casio digital piano, especially in this price range. "Expression" means that you can produce subtle mellow tones when playing the keys lightly or big bold piano tones when playing harder and more aggressively that I have never heard before in a Casio portable digital piano. As you press the keys harder and harder the sound brightens up and becomes more lively to the point where you can hear the "virtual" more lively to the point where you can hear the “virtual strings vibrate more & more offering a range of grand piano tone not available in any other portable digital piano under $1000 right now in my opinion. It really was amazing to play and hear and almost could not believe it the first time I heard it...it was that good. When I connected my small external stereo powered monitor system to the PX-S3000 by plugging into the piano audio outputs, the grand piano sound coming out of those speakers coupled with it also coming out of the piano's internal surround sound stereo speakers system was very full. It is important for me to point out that although the piano sound is really impressive in this new model and can fool some people into believing they are hearing a real acoustic grand piano, the fact remains that the piano sound here is a "recorded sample" that is produced electronically going through speakers and so there are still these limitations that prevents it from really being an organic acoustic grand piano, especially for those who play real grand pianos. Nevertheless, the bottom line is that this new PX-S3000 sounds and plays more like a real piano in my opinion than any other brand or model under $1000. With regard to the "polyphony power" in this model, 192 notes of power is more than sufficient if you are playing single instrument sound and also layering 2 sound together for most of the instruments. However, I did hear a bit of "note dropout" when using some specific instrument sounds layered together. When I test digital pianos for note dropout I do my best to play as many notes as possible together with the most memory intensive instrument tones layered together along with using the sustain pedal to its maximum potential. When doing all that at one time I pretty much expected a bit of "note dropout" because of the strain I was putting a the processor chip, whereas few other people using the PXS3000 would ever do that.
What that all means is that more the vast majority of people, there is plenty of polyphony processing power in there. As I mentioned earlier, Casio has a special app to interface with the many features of the PXS3000 so that you can more easily access and control certain aspects of the instrument including the organic elements of the acoustic piano sounds in this model which Casio calls "Acoustic Simulator."
This would include adjusting the sympathetic string vibrations, hammer noise, resonance, and other aspects of the acoustic piano sounds. This allows you to customize the acoustic piano sounds in ways not previously available in past Casio models or in any of the competitive brands in the way they are done in the Chordana app. You can also customize the "key touch sensitivity" levels in the app so that the piano sound responds to the type of touch you have (light, medium, heavy, and in-between). Some people will like using these "customizable" features and other people will not care and want to play the PXS3000 piano sounds just as they are.