Scott, welcome. Yes, you can use the extra set of left/right outputs on the C-1 to drive a subwoofer amp. You could either use two sub cables or use a Y-adaptor and one cable. Before you get into that though, maybe experiment with the positioning of your M80s. They have very strong bass and if you're going to use them for stereo music only, it might be satisfactory for music except for 16Hz pipe organ passages.

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Enjoy the music, not the equipment.