Anthony, since you refer to 12' ends, I assume that you meant that the room is 12x20. It would be better to move the seating at least 3' forward. You'll not be able to have more than about 10' of separation of the mains and a good rule is to not have the seating much farther away than the separation. Mount the QS8s on the side walls about 3' above ear level, with the left QS8 at the back edge of the glass and the right one directly opposite. This should put them maybe 2' farther back than the listening position.

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Enjoy the music, not the equipment.