Sat, since you prefer the more direct sound of the M22s to the more diffused sound of the QS4s as side surrounds, it's likely that you would have a similar view as to back surrounds. If you still have the QS4s and a spare amp to drive back surrounds you could listen to them there. If not, it seems likely that you would also have a preference for one or two M2s or M22s in back.

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Enjoy the music, not the equipment.