Hi gj,
Because of the multi-directional dispersion of the QS8s, they are very forgiving of asymmetrical placement, so no, it wouldn't matter if the rear QS8s were higher up and angled down slightly compared to the side QS8s.
You have a very large room, so I'd start with four QS8s, two on the side wall and two at the rear using the Axiom ceiling brackets. I think using four QS8s will provide you with excellent coverage and an immersive surround field. Some enthusiasts add an additional pair of side surround QS8s in large rooms.
The "angling down" also isn't critical with the QS8s either.
My own QS8s at the sides are not at the same height and in my experiments it made no difference in the creation of a deeply immersive soundfield.
You could also experiment if you like with the placement using a couple of stepladders to temporarily position the QS8s to see what, if any, effects there are with changing position.
Regards,
Alan
