I have the same problem as you with the Bryston site, and in general, all their electronics. They shouldn't listen to me though. I'll never buy because it's just too expensive.
Based on the published M80 sensitivity, at 14 feet away and 1 Watt input, the M80s will push out somewhere around 83dB of sound pressure. That Yammie is good somewhere between 120W to 160W. That gives you about 21dB of headroom allowing the M80s to get pushed to peaks of 104dB. Of course how your room is damped and how loud you like to listen matters but 21dB gives you good headroom. I consider 83dB to be a moderate nominal listening level so even if you listen 6dB higher you'll still have 15dB of headroom.
I am not at all sure the analysis above holds for M80s with HP drivers. You really need to consult with Axiom about that.
