There'd be very little difference between the M60 and M80 as far as amp requirements, so don't let that affect your choice of speakers. In Yamahas at that price or a little less I'd suggest that you consider the new 2400 instead, primarily because it has the YPAO automatic room and speaker equalization. Also note that the latest version is now being shipped with the DPLIIx upgrade.

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Enjoy the music, not the equipment.