Hey BigJohn! Here's a fellow Texan!
I am not technically oriented, so don't take my statements to the bank. But, I tend to think of the amplifier as the more likely source of distortion than the speakers, though I can't imagine you'd be pushing the 755 to it's limits. I bring this up just to remind you to be sure of the source of the distortion. I'd hate to have you replace your speakers and still hear distortion.
Here's the poop on the M80s and M60s. They both sound very similar (same midrange qualities). But, the 80s have a slightly lower frequency response (34Hz) than the 60s (37Hz), and will play louder. The 80s are 4 ohm speakers and the M60s are 8 ohm speakers which should be a little easier load for your amplifier (though I doubt the 755 would have trouble driving the 80s). Some have had trouble achieving proper placement with the 80s, describing them as "finicky"; some have NOT had this problem (OK,wid?).
I do not think the 80s would be overkill in a room that size. But, at a distance of only 8' from your TV, the 60s would be able to comb you hair, and would, I think, be "sufficient enough for your listening purposes." However, if you listen to music at reference level for any length of time, I'd look up the number of a good audiologist.
I've never heard the RTI-55s, so I'm unable to compare them to the Axioms. But, the Axioms can be positively described as "accurate," and "detailed." It's possible you'll hear things in your favorite CDs and DVDs that you've never heard before. They WILL expose a badly mixed or mastered CD. They are NOT referred to as "laid back."
Others will, I'm sure, comment and correct any misinformation I've stated.
Good luck, and keep us posted on your decision.
