Rat,

Sorry about the delay. I've been out of the country (sigh...again). The most noticible difference between the M200 and the 755 that I was able to discern was a lack of dynamics. There just seemed to be more "punch" and control over the speakers from the 755. The 755 also seemed to result is a wider and more realistic soundstage.

I haven't heard the 2200 or the 7500 so I can't say for sure that those differences still exist.

It's not just about output power.

Cheers,