@CyberGene Nice romanting playing! 👍
As an owner of Numa Compact 2, I'd say that engine of the X Piano is an "upgraded" version of what the Numa can present.
The pianos are harmonically richer, when it comes to resonances and overall sustain, there's as well the damper pedal sound included. I prefer it a little bit more silent than what I'm hearing, but it's cool and realistic.
The Rhodes pianos have more bite and more dynamics than the one in the Numa, I feel like the Numa Rhodes is just the same sample with different volume, there's not a lot of dynamic in the tines and bells - per say you woudn't get more bells/tines if you hit the key harder, which is implemented in the X Piano and I dig that. I also love the fact when you hit it harder it's on the edge to get this "break-up" Rhodes sound which makes it really authentic.
The FM pianos are a bit weird and strange, they feel like a "demo"version of the Yamaha DX7 with not enough stereo and harmonic content, although they will be fine when played live.
As far as I heard from the synths, the Oberheim OB-X sound was cool, then the Pad as well and in the end you played a MiniMoog sample which also sounds nice.
My overall feeling for the engine is that for the price range has a decent quality, but is not as top-notch as the Yamaha CP one or an expensive sophisticated VST library, so I'd say 7/10 for the sample quality.