Try the Yamaha first with the M80's and if you notice clipping or that the receiver shuts down than go with another form of amplification. If not, stick with the receiver. If your current Yamaha receiver has pre-outs and the features you like than I would suggest going with a 2 channel amplifier for the M80's.

If you do set up the M80's with the Yamaha, keep the impedance switch at its highest setting possible (if it has one) which will be either 6ohms or 8ohms.

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne