Update: Went to tune in the disc drive, managed to get the disc spinning, read, and playing, but no audio from my PVM speaker.
I do however faintly hear audio from the headphone jack. Based on this, I'm assuming I have another amplification-related problem.
I've checked the DAC with my Rigol DS1054Z oscilloscope, the audio is present, I've traced it from there to the 4560 Op AMP on the top of the board, yet I'm having trouble finding the next spot in it's path.
I'm learning a lot of stuff working on this Duo.
Edit: Figured it out! Had a via out that kept the 5V rail from making it to the pin. (I traced it out first) Soldered a jumper wire from the 5V rail to pin 8, and she's working perfectly again. =)
Edit: After checking another thread, I checked a few caps in the audio section of the board and found that C162 has no voltage on the positive side. I think I found part of the problem. =)