As has been suggested above, the farther you are from the source the harder it is to pinpoint the location of various instruments. I'm sure the conductor of an orchestra has no problem discerning the 1st violin from the 2nd, although the same person might be challanged from the 25th row. After spending many hours and a small fortune putting together a high-end system, I would argue that we have a right to expect something that in many ways surpasses the live concert experience. I agree with Jeffery that imaging is the minimum that we should expect from a good system, and that "tonality, clarity, and dynamics" are more important objectives, but there's no reason to leave behind the spatial cues provided by stereo to achieve these things.