I think you will find you won't be running the Denon at 0 or +5 much with the Axioms, they are more sensitive than many other speakers, I hit about 98 db cleanly with my old Denon 1804 and that was very loud in my room , I can now hit around 105 deepnding on the material with the 3808 and that is still around 0 on the volume control.
I trust your MP3s are ripped to at least 128K or higher, otherwise you will find them to sound bad. The M60s are slightly more forgiving IMO and might have been a better choice to stick with, I think I would have stayed the course and had a listen to the M60s as to whether or not you NEEDED to upgrade to the M80s, if your main source is lower grade MP3s.
