I'm not exactly sure what is causing the issue, but whenever multiple channels are playing simultaneously on the N163 portion, all of the instruments seem to "combine" into one wave, completely ignoring the wave each of them were assigned. Take a look for yourself in the FTM below. Pay attention to the N163 portion. Play all 5, then disable the 5th one, you'll see what I'm talking about. It will also sound really ugly at the last few frames. Please help.
