(Edit: update to add text notes, fix a few typos. Also, I made the pictures bigger, so that they could be copied, zoomed, and viewed easier...but I may have overdone it! If they're objectionable, let me know...I'll reduce them a bit!!!)
Finally! Resolved my errors....oops, I mean questions (yeah! That's it---"questions") on the actual DUO audio circuitry.
Abbreviated schematic of DUO audio circuitry, part 1:
Abbreviated schematic of DUO audio circuitry, part 2:
Charlie