After modding my nes to play the extra channels of sound with the powerpak and loopys mappers i thought it would be cool if this was possible.
It would be a great way to enjoy the mod and enhance a game.
Well you'd have to make "fake" mappers that support the channels. In theory its possible but its alot of hard work.
Sure, you could patch the sound register writes to routines that convert it to anything. I do that for visual effects. It's a matter of replacing STA $4xxx with JSRs to appropriate bits of code.
That's a good idea, I should have done that with Squeedo. That would be fun for editing waveforms and hearing it right away.