Whether or not to go with M60s over the M22ti's really depends on your personal taste in volume levels versus how large your room is and how far back you are from the main speakers.
I do much of my listening using a pair of M22ti's and the EP500 subwoofer in an average-size living room (19 x 13 x 9 ft.). I've always emphasized that the M22ti's have the ability to play surprisingly loud so long as you aren't trying to fill a huge space, but last night viewing the DVD of War of the Worlds with the DTS mix, I was dumbfounded. The low frequencies on the DTS mix are astonishing over the EP500, but the dynamic peaks in that soundtrack didn't seem to strain the capabilities of the M22ti's. I have a pair of M80 towers as well that I can switch instantly to, but I was so transfixed by the chaos and dynamics of the soundtrack that I kept reducing the level for fear of disturbing my lead-footed neighbours upstairs .
I may replay the sequences using the M80ti's but in my smallish living room (2200 cu ft.) I had no complaints about the very loud dynamic peaks from the M22's with the EP500, VP100, and QS8s. If your room is of similar size, adding the M60s may not result in a really significant audible improvement. Note that I don't listen at levels as loud as several of my Axiom colleagues.
As to subwoofers, if you're in Canada, Axiom's EP175 or EP350 deliver tight, powerful bass, albeit not in the same class as the EP500, but impressive nonetheless.
Axiom Resident Expert