The absolute best system I ever heard was installed in a large, circular room with a heavy domed ceiling, baffles around the walls, and a moderately thick carpet. Not a standing wave in the place, and excellent sound quality from almost anywhere in the room.
If you could...
If you could build a listening {not theatre} room that you did not need to use for anything else, what dimensions would it be? Ceiling height, etc... for optimal sound quality. Assuming an above average system.