So here are my latest observations and loose reasoning/weak hypothesis:
We watched a dvd tonight and the peaks were up to 107 db (volume setting was +4.5 db) before mild almost subtle popping sounds kicked in, keep in mind that loud, nasty popping sounds were evident at 90-100 db before with the 8 ohm setting, so this was a definite improvement, although clearly not a solution. Also I should point out that I would not have noticed these sounds currently if I had not been trained to do so by previous experience, they were mild rather than obnoxious by comparison.
All cases of "popping" sounds going back the past 2 months or more (?) have only occurred during HT LFEs, never during music playback, even at similar or even higher db levels.
It makes no immediate sense that an LFE would cause a high frequency pop like a gunshot (not really a close example but just for comparison sake).
I have no subwoofer (waiting for Godot) and it has been documented that the M80s are limited with regard to the LFE frequency range.
I suspect that with no subwoofer to receive deep LFE output the preamp has nowhere to discharge the power output and this may cause the popping distortion I am experiencing during LFEs.
Everything else besides LFEs sounds perfect, actually LFEs sound smoother, louder, and better since I set the 663 to a 6 ohm output setting; although I couldn't swear to this since I have obviously done no DBT, it seems unlikely to attribute a much softer almost negligible "pop" to listener artifact given a 10 db increase in SPLs.
Perhaps others know better but I have no way to check this out except to wait a few weeks until the sub comes; of course this could be massive wishful thinking on my part since I am hoping this problem goes away at that point, or that at least I achieve something closer to the peak volume I would like have in play without the sonic defect kicking in.
JohnK, I don't think this in any way contradicts the info you have shared, given that according to my understanding it is not a good idea to run an amplifier at high volumes without a resistor downstream to discharge the power output, because then the power has nowhere to go other than toward some form of implosion.
Perhaps my thought process is way old school or off base, perhaps they have error correction built in to correct such issues nowadays, if so I'm sure you will all let me know the error of my ways (of thinking), at any rate the system is working much better and I will have nothing to report until the sub arrives, I will let you all know if I achieve greater workability at that point.
