If you are maxing out the 607, then don't presume it is the M80 lacking the bass. At loud volumes, you need a lot of power, and bass notes take more power than highs. Anywhere near full power and you are clipping hard, which is part of the reason you are lacking some bass. I had a similar issue with my Denon before adding a separate amp to the mix. Now I could sell my sub except for subterranean LFE in some movies.

Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire