Hey, Pat - how's it going?

A few things come to mind. First, you could swap the M200's pretty easily to see if the problem follows along with the right channel's amp or stays in place - I think this would be a good and relatively quick way to test the amp part of the equation. If the problem stays on the right side, you might even try swapping the left and right speakers to see if it's something internal to the 750 (weakened solder joint, for example). Second, I wonder about running analog stereo from the DVR to the 1050, although I'm not sure what that would prove. A related test would be to move the DVR down to the theater and hook it up to the 950. If the problem followed it, you'd know that was the source of the issue without having to dismantle the big system. Lastly, I'd try running some radio or a DVD in the system just to see if it shows up at all with those - which could be done in parallel with some of the other tests if the opportunity presents itself.