Steve!
Peter, I've got a sneakin' suspicion that wall just behind the couch is a half wall. Hope so. If it is then the rear surround placement would be OK. If not, then Peter's suggestion of a single QS8 above the door is a good one.
Steve, the party line is that it's preferred that all speakers match sonically as much as possible. This usually means "use speakers by the same manufacturer." However, matching the front 3 speakers is considered to be considerably more critical than matching the surrounds to the front 3 due to the limited amount of information the surrounds are required to carry.
I have no personal experience using the QS8s with speakers other than Axioms, so I cannot say how well, or poorly, this would work. But, I'm aware of several who use them with other brands, who appear satisfied with the results.
Though I've not heard a large number of surround speakers, the QS8s are, far and away, the best I've ever owned, and I'm completely satisfied with them. Here is my standard QS8 statement:
The QS8s are startlingly immersing. My standard comment on the QS8s is "the thing I notice most about the QS8s is that I DON’T notice them." They do a wonderful job of providing the surround experience without calling attention to themselves in any way. They do not distract from the movie. 
