Thanks for your inputs.
Apologies for misspeaking about the "HD Input"
What I meant was that I had gone to HD video and surround sound. You're right. This unit does not support HDMI, only the 5.1 ch. audio.
To be more clear about my problem....the 5.1 audio (using optical...pro logic, etc.) was working fine, including the subwoofer output (and LFE indicator), both before I discovered the bad solder connections problem (albeit the rear amp output was greatly reduced because of the bad connections) and after I fixed it . It's been recent, after enjoying about a year of great surround sound, that my current problem with the subwoofer occurred. So, if there is an overload issue, it's happened recently (BTW - not obvious there's any kind of adjustment for that).
I do have the service manual and checked the schematics. Lots of complex h/w (audio DSP, A-D/D-A converter, a few op amps, etc.). Not sure of where the subwoofer info is "decoded" (my guess is the audio DSP). Somehow, it seems the sub is processed differently when in 5.1 vs "normal" (maybe that's a "Duh!" statement since the sub is fine in stereo mode, but acts up in 5.1
I only have 1 5.1 input active (DishNetwork DVR) and it's possible that could have become the source of the problem. It might also be one of the audio opamps or associated components or related solder connection issue (I should be so lucky) causing it. I could also shift the DVR to another input to see if it's input channel related (tho, I'm guessing not).
Thought maybe since so many people were familiar with the Sony solder problem, someone might recognize this one, as well.
Thanks again. I'll repost if, and when, I figure this out. Meanwhile, time to pull otu the scope and DMM and/or find another known working 5.1 input.