First off, if I had a choice I would change the room that the piano resides in and make it more acoustically acceptable for an acoustic piano. When I built my home theater I did exactly that. I spent more time and money making it acoustically correct then on any other aspect of it. I also own a professional recording studio so I am well aware of acoustic treatments and the needs for them.
But, my wife would definitely have some choice words if I were to place carpet over the finished wood floors and put acoustic baffles over the windows that overlook the lake. :) So... I have to compromise. Placing the foam in the underside of the piano seemed to be an adequate compromise. I can still open the top of the piano and also still have the ability to adjust the volume of the 850 itself.
There are also different circumstances that call for different volumes of a piano or a stereo as referenced. At least in my house there are. I have a "listening" stereo system and a whole-house music system. When I want to do critical listening I use my stereo system and have the volume at a level that is appropriate for what I am listening to. When I have guests over I use the whole house system and have the volume at an appropriate level for the activity that is occurring. It is the same for the piano. Even when hosting parties I typically corral the guests for a period of time and play the piano at full volume so that they can appreciate it. But then I turn it down so the guests can enjoy each other's company as well as acoustic background music.
If I were to invite guests over for the sole purpose of listening to the piano then it would be a totally different story. They would not talk as the focus would be a piano performance. But I cannot imagine doing that unless a pianist is actually playing the piano. Who would want to sit and watch the disklavier play for any length of time unless it was using Yamaha TV for a live experience.
Again, IMHO as it pertains to giving respect to the original pianist's performance, we will never be able to replicate the performance in our houses. IMO, it is technically not possible. Any time you capture an analog source and convert it to digital, whether it be a movement like a pianist striking a key or the music itself, the complete analog signature is not captured. Pieces of it are captured and the rest are interpolated. It would be like saying that listening to a MP3 is the same as being at the concert. Even "lossless" audio is truly not lossless. It just has less loss than other methods.
Joe