I intended on purchasing the m60's back in '07 when I was looking at axioms. I was able to find the m80's for an audition but not m60's. After hearing the m80's I knew I had to have a pair. I haven't heard the m60's so I can't offer much advice other than I don't think you can go wrong with either one.
I'd vote for the m80's simply because they have given me the exact listening experience you are describing (great imaging, nice full musical sound, clean midrange, etc.) for the last 3 years. If I owned the m60's I could probably say the same thing about those speakers though.
While the planned listening distance isn't all that far for you, it sounds as though a nice equilateral triangle would be formed which should give you great imaging.
I have never noticed any strange sounds or imaging problems with dual mids and tweeters.
Also, I suggest you have 12" of clear space between the m80's and the back wall since they are rear ported.
