This is an interesting question.
I have a Steinway M, but with a MIDI strip, so it can also be used with a synthesizer as a "high end digital piano."
Over the years, I have experimented with a lot of things, including Audio Research and Levinson into my Tympanis, thinking it would be wonderful, warm, room filling and more natural to hear the digital piano this way.
In the end, however, this was not satisfying at all and I used active Genelec monitors sitting on top of the piano for best results.
Although a bit forward relative to my usual hi fi taste, there was something about 1) the active configuration, 2) clarity of the biamping and 3) the ability of those speakers to attack and sound dynamic that made them more fun to play with the digital synthesizer.
This was true whether for acoustic piano sounds or for more contemporary synthesized sounds.
Also, on top of the piano gave a better illusion that the sound was actually coming from the piano, rather than from a stereo in the room. For me, this proved to be as or more important than the actual sound.
So I would agree with Chayro and others!
Enjoy your pianos, but you could spend your money on other things.