I don't have the hardware to test it, I know some people who do, though. I'll put this code into a ROM and post it here soon.

Setting D7 of $4017 should be OK from what the docs say, all I know for sure is one of my programs that used the DMC IRQ was working when I set it to $C0.

There would be some variations with exactly when the IRQ code runs, since it will have to wait until the CPU finishes it's current instruction (usually varying between 5 and 2 cycles long). I don't know how noticable that would be, but an idle loop of NOPs might be helpful if that's the case.

Yeah, playing an NSF on NES requires a small bit of control code. All the vector-related stuff must be handled by that. I was able to play an NSF with IRQs on FCEU, but it didn't work on some NSF-only players that I tried.