Dan, it isn't entirely clear what you're asking. You used "combining", but then just described using 2 of the 5 channels of the 7000 for mains and a 3rd for the center, which is just a normal setup. If by combining you were asking if some unused amp channels could be bridged, the 7000 has no provision for that; or, were you possibly speaking of bi-amping the M80s.

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Enjoy the music, not the equipment.