Also own m60s and I would also question any view that they are bass heavy at any volume. They have very good bass extension but the mids and highs are equally apparent.
If you take a look at the frequency charts Axiom provides, I think you will see they differ very little from the M80s in that they throw an impressively flat curve and are balanced all round.
In the end, buy what makes you feel good but audition if you can. If they have already signed up in the audition list, then I think they would enjoy accommodating you for a listen.
