Some might disagree but that some of what you are hearing is the inadequacy of MP3 recorded compressed all the way down to 192 KBPS. As Mark mentioned, purchase a Dianna Krall CD or some other famously well recorded CDs such as Pink Floyd's "Dark Side of the Moon" or my personal favorites for musical demos, Dire Straights' "Brothers in Arms" or the Dave Mathews and Tim Reynolds "live at Radio City" concert DVD (or BR). The first has a greater range of sounds and frequencies to evaluate but the second is such a pure recording of two guitars that it can bring tears to your eyes on a good system.
Also, take the time to listen to them over a longer period of time. Try not jumping back and forth between the Canton's and the M80s. I find that the brain takes time to adjust to new sounds/speakers. Every time I come home and listen to my M60s after listening to a car radio for a long drive, the M60s sound a bit off. After a few songs however, they return to amazing musical bliss. It does take a while to adjust.
Fiddle with the placement, source, etc as others have suggested and try listening to the M80s only for a couple of days. then try the Cantons again. Since you still have time, you can return whichever make you less happy in the end.
Good sound needs to equate to your personal happiness so whichever works best for that.
With great power comes Awesome irresponsibility.