I'm really confused.
Do you already own the speakers (and you're just looking for comment on placement) or are you still in the purchase process for any of them?
I really wouldn't consider putting "on wall" speakers "between the studs" or "angling" them. It's not going to look good, and you might actually make them sound worse.
If you're really set on 7.1 in that room, I'd put the rear speakers actually BEHIND the couch and firing forward. I don't know what is off the chart on the upper left. I'd definitely put one of them in that 42" high wall to the left of the stairs - maybe just do 6.1 with that position.
I think you're going to get truly nasty early reflections from both the left front and right rear speakers as drawn.
I'd very strongly urge you to just do 5.1 with the QS surrounds in that room.
