That's interesting that most of you run the M80s with a sub. Wouldn't that beat the purpose of having the 80s instead of the 60s since the extra bass given by the 80s will be useless in that case?
IMO it sort of defeats the purpose of getting tower speakers in the first place for most people. I listen to lots and lots of Trance with very rapid bass beats. I find the bass is much clearer at 160BPM when played from just the M80s and not the M80s + sub. Could just be a byproduct of not being able to exactly match the distance delays, crossover issues, room resonance being excited by the lower bass of the sub or a combination of those and other things.
For the music where I kick the sub in there isnt a rapid beat to deal with so I sounds fine.
There is some very interesting discussion here! If you look at the 2 graphs Axiom provides for the M60 and M80, you can see that for the most part they are identical speakers with the nod going to the M80 across most of the frequency spectrum by about 2db (confirmed by the 93db vs 91db ratings of the speakers). They are both basically flat down to about 80 Hz, lose about 3 or 4 db at 60 Hz, and lose about 5 or 6 db at 40 Hz. Lower than 40 Hz, the M80 gains it's advantage over the M60. At 20Hz, the M80 can produce a signal 4 times more powerful than the M80, but it is still 20 db lower than the source (almost inaudible). And that's I guess where the sub comes into play.
If some of you remember my older posts, I played around a lot with REW and the Behringer BFD to try to even out my bass response and tame my room. I had a notorious room resonance in the 60 Hz range which caused my bass to feel "slow" (as Grunt said) and "muddy". Although I spent a lot of time with this, in the end I found an easier answer which worked for my room and my setup. I simply lowered the XO frequency in my receiver from 80 Hz to 60 Hz. In doing so, I cut out my subs and my mains trying to reproduce this frequency (which both can easily), and really dropped the room's contribution to this frquency. The end result was a bass sound that was much more "tight" and "quick". The good thing is that the sub is now there to handle the frquencies that both the M60 and M80 are not particularly great at (frequencies lower than 40Hz).
As a side note, I tried lowering the XO to 40 Hz, but IMHO and in my room, I felt it made the resultant sound "thin", so I switched it back. Keep in mind however that all of these measurements and adjustments were made when I had two EP500s. Now that I have two EP800s (twice the amount of 12" drivers), I may reinvestigate the possibility of lowering the XO to 40 Hz.
There is a great article here on subwoofer XO crossover settings:http://www.hometheaterhifi.com/volume_9_3/feature-article-multiple-crossovers-9-2002.html
But, to get back to the OP, I think either the M60 of M80 would be great for listening to music. They have almost identical frequency responses above 40 Hz, and that's where 95%+ of the frequencies in recorded music is positioned.
I think I'm learning over the years that I have to treat my subwoofers as subwoofers, and not woofers.