Dudditz,
Apart from the dreaded "6-ohm switch" that JohnK has advised you on (leave the Yamaha at the 8-ohm setting), you should consider the total volume of your room and your taste for very loud playback levels, which the M80s are capable of when powered by large separate power amps. If your room is of average size (2100 cu ft.) to somewhat larger, the Yamaha will have ample power output to achieve loud, clean playback.
But if you have a large room (4,000 to 8,000 cu ft) and you like really loud playback (95 dB SPL and up), you are right to consider the Crown for the M80s. Several of my colleagues with M80s enjoy what I call "deafening" listening levels of rock n roll in large rooms, and they use either monoblocks with 250 watts per channel or something like the Outlaw multichannel power amp.
My own M80s in a typical 2,100 cu ft room are nicely powered by my modest H/K receivers's 80 watts per channel. I seldom run my system peaking at greater than 96 dB SPL at my listening location (subjectively that level is termed "very loud").
Always look at the total room volume, furnishings, listening distance and personal preferences with playback levels.
Regards,
