You'll get both sides of the argument in about equal numbers I predict. Yes the M60's will probably be just fine, better than fine, but if you can spare the few hundred extra bucks, why not go for the flagship M80's? If money is a little bit of an issue, then you'll be very happy with th M60's.
I have the M80's, my friend has the M60's, they sound very similar, the M80's have a little more bass. He thinks my M80's sound a little smoother at the high end, I didn't notice that. To me the bass on the M60's sounds a little boomier than the 80's, but still very good. I have not heard the two models together in the same room, so hard to say.
The Yamaha should drive the 80's just fine, a little more power wouldn't hurt though, and if you are prepared to spend the money then go for it. My buddy with the M60's is now wishing he had the 80's only because he can afford the extra cost and why not get the top of the line? so you aren't worried about what you are missing out on?
