Walker, welcome. For a 5.1 setup without back surrounds it's best if the side surrounds can be positioned slightly farther back than directly to the side, to lend a little phantom "back" effect. In your situation this suggests mounting the QS8s on the rear wall about 2-3' above ear level and spread as widely as possible, just a few inches from the side walls.

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Enjoy the music, not the equipment.