If the system were for music only, I would strongly recomment the M80s, skip the sub and call it a day. They are noticeably better than the M60 on their own because of the bass extension, more clarity at the top and a little better mid-bass.
However...
I was like you, looking for mainly a music system, but was surprised by how much good surrounds and a good sub added to the movie experience.
If it is beween the M22 and M60 with a sub, I would go with the M22 + sub. I had a chance to listen to all the combinations at Axiom, and was surprised to find that I had a hard time telling the difference between the M22 + sub and the M60 + sub (aside from the obviouse bass extension a sub gives you. This was with V2 product.
No matter which you choose, you will be very happy.
