M22s are overkill for height speakers if you want to go with a direct radiating speaker the M2 is fine. IMO the QS8 works better as a height speaker since it’s designed to better produce ambient sounds which is all that’s coming out of the height channels.
As for placement take a look at this suggest placement by audyssey:
http://www.practical-home-theater-guide.com/image-files/audyssey-dsx-7.1.gifThey suggest placing the height speakers farther out than the mains. I found that this also worked best in my room.
