I was playing with gctool and I opened up the donkey konga gcm and i browsed through it and found .mid files. Excited, I extracted the gcm and played one of the mids and it was a rhythm track, not the actual song.

I wonder if you edited the mid with an editing program, if it would change the rhythms in the game. I'm pretty sure it would, but I don't have viper gc or pso to try it out.