Given the compromises, I wouldn't even do rear surrounds in that room. I would think flush-mounting of the QS8s would be fine, but I've never tried mounting them that high. Of course, I'm also much closer to my QS8s.
I probably wouldn't bother with the EP175s, either. The chances of them being effective seem pretty slim to me. If you can't accommodate a sub in a room, how about a ButtKicker? I just got one, and it adds some nice impact for movies. If you can hide it, that may be a way to cheat and get some low-end "feel."
