Stoney, there's really no such factor as "optimally" powering a speaker. As long as the receiver can deliver as much power as the speakers would need at peaks(which is less than is sometimes thought, especially with the M80s which are slightly above average in sensitivity), nothing more can be accomplished. Keep in mind that, for example, 200 watts represents only 3dB more in maximum sound level than 100 watts; if 100 watts could play a brief peak at say 110dB, 200 watts could play it at 113dB. Unused maximum power capacity is simply that: unused.

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Enjoy the music, not the equipment.