First, a bit of background. I've had my CLP115 for about twenty years. I don't use it a great deal, just when the mood takes me. I'd begun to notice though that the keys seemed to have become noisy and had a hard landing. I just assumed I needed a new piano so started looking around and it seemed I would have to spend in excess of £2000 to get anything worthwhile. During this research I came across a Youtube video of someone replacing the felts on a similar model, discovered I could easily get new felts from the dealer I bought the piano from, so went ahead and replaced the felts. Doing that showed me how easy it is to take the piano apart and also how much space there is inside. I've also now replaced the rubber contacts for the keyboard so I suppose the action is as good as it ever was.
As I was now looking at piano stuff online, something I hadn't done before, I came across VST's and Pianoteq and in particular @navindra 's excellent posts on the Pianoteq forum about running Pianoteq on a Raspberry pi. So I followed his guidance and installed Pianoteq on a Raspberry Pi 400 (also on a Macmini) but because the CLP115 has no audio input capability I needed to use external monitors (a pair of M-Audio BX4's). However I found the placement difficult and I really don't want the clutter of external speakers, ultimately I want the piano to stand alone as it did before. To connect the computer to the speakers I had bought a Behringer UCA202 DAC interface which is very compact and I thought if I could get a similar sized amplifier and suitable replacement speakers then I could put it all inside the piano. I identified a Nobsound NS-10G Pro 100w amp as being suitable and also bought a pair of Alpine SXE 4625 two-way 60w car speakers. Speaker choice was very limited as they needed to be an elliptical shape to get the maximum size possible in the space available.
Installation was very simple - I just removed the existing speakers and their wiring and inserted the Alpines together with the Behringer and the Nobsound (temporarily velcroed in). There is a convenient metal plate that holds the piano's three MIDI ports and I was able to hacksaw a chunk out of it to create a hole for the cables. There is a USB cable from the computer to the Behringer DAC and a power cable for the Nobsound amp. MIDI out from the piano to the computer is via a MIDI to USB cable.
When I can get a Raspberry Pi4 (more compact than the Pi400) I will also put that inside the piano and as I can control the whole shebang from the piano keyboard (see this thread https://forum.modartt.com/viewtopic.php?id=9196) the only visible change to the piano will be two extra cables (and a screen if I want to read online music).
I have a £1500 Naim Mu-so 400w hifi music streamer but I much prefer now to stream Spotify through the piano. I'm no expert but it seems to give a much better hi-fi experience, perhaps because the speakers are ideally spaced and effectively in a large resonance cabinet.
I think the most basic models of digital pianos, like the CLP115, are best suited for this treatment as there is more space inside than in higher end models with lots of different controls.
In the image below the Behringer DAC is the silver object on the left, the Nobsound amp is the black object on the right.