Sam, welcome. Since you'll have back surround speakers, the side surround speakers won't have to help with the back effects. The suggestion to have the side surrounds a little farther back than the listening position, to help with back effects in a 5.1 setup without back surround speakers therefore doesn't apply. If possible you should have the QS8s directly to the side of the listening position, to maximize their side surround function. This isn't critical, especially with very wide dispersion surrounds such as the QSs, but if you could move the seating a little forward without compromising the room arrangement it'd be helpful.
