In Russian we often call the piano as "Fortepiano". Obviously, "forte" means "loudly" and "piano" means "quietly". To me the common problem with digital keyboards is that some of them do not really let you enjoy the both ways of playing - "forte" and "piano". Yet, I've been more or less satisfied with Yamaha's algorithm, which they call as "dynamic filter". Also, we know about multisamples, which also helps.

I'm not sure if I can judge by the demo, but I have an impression that so far this Steinway tends to be more "forte" than "piano".

Today I've recorded a piece on my PSR-S950, the factory piano is used (a brighter one) with a dark layer behind it:



But, frankly, I'm a bit bored with this factory sound, so I understand that what you're doing can be quite a big deal.