Griff, I'd understood you to say before that you were getting M80s and had already arranged the sale of your M60s. In any case, if you have a significant distance behind your listening position, which for M60s I'd suggest to be at least 6', they can certainly serve as back surrounds(definitely keep the QS8 sides). Another thought would be to use the M60s in a separate setup in another room(bedroom?).

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Enjoy the music, not the equipment.