Nellie, welcome. The Epic 80 7.1 system that you're considering should give you excellent sound in your rather large room. The 4600 should drive the M80s with ease and there'd be no reason to instead use M60s on that account. Keep in mind that the M80s are actually a little more sensitive than the M60s and therefore use less power for a given sound level. They constitute a relatively easy 4 ohm load.

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Enjoy the music, not the equipment.