Very nice, bit of nostalgia :]
sounds a lot like the GBC version of the track!

Bit of constructive criticism:
I'd suggest setting the polyphony on each of your synths to 1, so they don't overlap with eachother. Also keep in mind that the NES had 5 distinct channels: pulse, pulse, triangle (which couldn't change volume - very important), noise, dpcm. None of these could play more than 1 sound at a time.