Hi RMC,
I absolutely agree with Mark about excessive line levels from your computer sound card overdriving the inputs on the Panasonic. I don't really advocate using computers for home theater playback of DVDs as the sound cards can be wildly variable in quality and generally don't meet the standards of audio-video playback gear.
As to the Panasonic, I have not used it. I'm somewhat apprehensive about digital amplifiers for wideband amplification, although if designed properly, they can be excellent.
It's certainly not a problem in the M3ti's. But I'm a bit concerned the overload distortion in the XR55 might have sent distortion components to the M3ti's. Your headphone test is excellent, but try borrowing a conventional DVD player (or CD player) and use the Panasonic's analog inputs to see if you hear any of the same problems with your M3ti's. If you do, call or email Axiom's service manager Joe Vassallo (joev@axiomaudio.com).
Regards,
