Although you still didn't specify how far from the back wall that you'll be sitting, with the length being 24', it may be a considerable distance. Even with QSs, side surround speakers shouldn't be placed too far behind the listeners. Depending on how far it actually is, mounting them on the side walls(if a wall mounting is possible) a couple of feet back may be preferable. A thought is to experiment with temporary locations when you get your QS8s.

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Enjoy the music, not the equipment.