Hi 1sweetspot,
Welcome to the Axiom Forums. Something is very, very wrong with your Denon setup. As JohnK has pointed out, your Denon's power output should drive the M60s to extremely loud playback levels without audible distortion.
It's easier to adjust the pink-noise levels manually using the Dolby Digital test signal built into the Denon. Turn off Audyssey, and use the rotating pink-noise Dolby signal at either 80 dB SPL or 85 dB SPL (75 db is too quiet to make precise adjustments by ear).
Pay special attention to the front left main, center, and front right main level settings in your Denon menu. Set them to 0 dB. I think you have all the level settings way too low.
Be careful about turning up the Denon volume control too high, as you may drive the amp into clipping which could damage the tweeters in your speakers.
Regards,
Alan
