Jeff, a significant factor is how close you'll be sitting to the back wall. If the QS8s are on the side wall they should preferably also be a little behind the sitting position to lend a little "back" effect. If you're going to be sitting right up against the back wall, there's obviously no room on the side wall to do this. In that case mounting the QS8s on the back wall and separated widely, almost to the side walls, is probably a good idea.

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Enjoy the music, not the equipment.