Chris, welcome. Yes, the QS8s are outstanding performers as surrounds. Since you'll be using the Sonys as back surrounds, the QS8 side surrounds should be mounted directly to the side of the listening position if possible, and about 3' above ear level. The back surrounds should be separated by about as far as the distance that they're behind the listening position, assuming that's enough to put them outside the listening position both on the left and right.
Those positions were pretty much what I had in mind. The Sonys will be about 7.5' behind me and about 6.5' apart. My room is shaped kind of strange. It is 15x20, but the corners are cut off to make it an elongated, slightly widened octagon. So I didn't want to get the rears too close to the angled corners. 6.5' still puts the rears slightly beyond the listening area, and about a half-foot inside with width of the fronts.
I had seen a few other posts day the surround should go 3' above ear level, but I didn't really think about it until now. When I'm seated my ear level is about 3' from the floor, so that means the speakers should be mounted 6' up the wall. That's higher than I have my current speakers, but I guess you know best.
I have 9-foot ceilings, by the way.
