Just move the wall back and your golden.
Kidding aside, I'm not so sure the M2s would have all that noticeably better highs. It looks like they both might share the exact same 1" tweeter and the cabinet shape does not come into play nearly as much for tweeters as for the other drivers. The only real difference is a high x-over of 2 KHz for the M60s vs. 2.7 KHz for the M2's, which actually means less highs in the M2 are being produced by the tweeter. (not implying they should be the same, I'm sure they landed on those numbers for good reasons)
But then again, I've never heard an M2 and I'm sure there are a hundred more factors at play, which puts me back to "I'm not so sure" in either direction.
Just thinking out loud, really I guess.
