Well I finally had a chance to crank up the system again today and was able to reproduce the crackling sound on the Fellowship of the Ring where the trees are being torn down around Chapter 19, if memory serves. When you crank it up there is this loud popping sound that is just not there at lower volumes. Today during this section of the movie the Yamaha spontaneously shut down. I have been suspecting the 663 since last week and won't be able to prove anything until I upgrade to a better pre/pro but I felt compelled to share my suspicions, which relate to the XPA2 as well, because perhaps the emo amp was going into protect for a reason. I never heard the popping sound on the XPA2 with the M80s because the amp would shut down, but when I hooked up the Polk 10Bs (to the 663 and XPA2) there was a popping sound as well as the speakers began to fry (burning plastic smell); I assumed this was because the 6 ohm 10Bs are rated at 250w max and the XPA2 puts out more power than that. You may recall I was using the intro to Hulk to troubleshoot the problem, unfortunately this contains a lot of electrical explosions so when I hooked up the M80s and the A1400 I thought a couple of the pops sounded a bit harsh but thought it might be accurate just too loud. The Fellowship passage is less ambiguous and suggests something is wrong.
The fix for now is not to play movies that loud (not something I want to experiment with much to avoid speaker damage), between 80-90 dbs is no problem, later I plan to replace the 663, still somewhat dragging my heels to see if the Outlaw 997 comes out in a timely fashion and is well received.
Although this is preliminary and still makes little sense I wanted to put this out so any who might be considering the XPA2 or 663 would know that my experiences with this equipment remain inconclusive, i.e., the XPA2 might pair just fine with the M80s given the right processor, the 663 might have some inexplicable glitches relating to "the curse of the Yamaha."
"If you try to turn toward it, you go against it."