Myles, although three identical vertical speakers across the front would be ideal, I can assure you from both theory and personal experience that an M22 would be excellent in that service.
If you're planning a 5.1 setup with side surrounds, but not back surrounds in a 7.1 setup, the QS8s should definitely preferred. If your reference to a "rear surround" indicates a 7.1 setup, some prefer a more direct speaker such as M2s for that purpose(especially if there's a considerable distance behind the listening position)while others say that the QSs are excellent all around. Depends on personal preference and the size of the listening room.
