If the piano is behind you, probably not too bad. Any room furnishings even curtains & carpet affect the sound. Get a copy of Robert Harley's book, The Complete Guide to High End Audio (2nd edition) to help with you system and media room. The piano cabinet definitely resonates, which is why a concert grand sounds fuller than the small upright piano in the parlor. So covering ir when not in use would help "remove" it from the room even though it is physically there. Temperature changes also have a big affect on string instruments tuning including the piano's strings.
Audio Gremlins and Musical Instruments
Many years ago, the fascinating Enid Lumley of the Absolute Sound and members of the Linn cult used to insist, amoung other things, that telephones be removed from the listening room to prevent their tiny speakers from polluting the sonic atmosphere. I am starting to design my next listening room and I would love to put a 6'3" piano in the room, behind my principal listening chair, not only for aesthetic reasons but too play along when I am in the mood. Could this be a major mistake? Does anyone have any experience with a piano or other instruments? I suppose a snare drum in front of a subwoofer might not be the best idea, but I have never seen musicians frantically covering the Bosendorfer with Shun Mook blankets because the program is switching to strings. Any ideas or comments would be greatly appreciated.