I've asked him - he doesn't want to share it unless he's getting some money for his time.
Did he give any sort of price range for it? I think people here would pretty gladly pitch in on a bounty for working VRC7 audio and fixed FDS audio.
Yeah, I've basically purchased all of the famicom games with expansion audio that I wanted to hear with proper audio (Lagrange Point, Gimmik!, Just Breed, Akumajou Densetsu, Esper Dream 2, Madara). It's understandably difficult to emulate such varied mappers accurately, but I don't want to deal with original FDS hardware in order to play FDS games with correct sound, particularly because if you emulate the extra FDS channels accurately, the fix will apply to all games.
If this individual wants to get paid in order to divulge his work that would lead to proper FDS audio, I'd gladly chip in some cash; let's proposition him I say.