I agree with you that above the window is not ideal placement of the QS8. They would be too high from your listening position and too close to the ceiling. Such combination could possibly not deliver to you the optimum sound from QS8's. If they are placed behind your listening position you may only need one M22 for rear center to catch the 6.1 effect. You may not even need one with that placement. But if you have decided that you really want a dual rear, then the only alternative is to place the QS8's a little bit forward from the listening position which is before the window.
I am also thinking of adding M22's for rear. Please let us know how it works out.
