No problems with the Denon, They are one of the companies Axiom recommends for the M80's. I have the same AVR and speakers and have had no problems what so ever. My older 1804 ran the M80s and even a load down around the 1 ohm range with out problems.
So far as the EP500 goes the general rule is the phase is 0, crossover on bypass, trim to flat and the the rest is upto you and the Audyssey. Most have said the Audyysey set the sub at -12 in the Denon, so they just bumped it up a notch or 2 to suit their own tastes.These are just starting points from here you acn try tweaking each one a little to see if it sounds better in your room.
