"Ice Mario and I worked together to make this a long time ago, and I have kept meaning to post it. Anyways, it's an open source sound tool for N64 ROMs, which lets you play standard format waves, and lets you add/change waves that are in the game already.
As a caveat, we never figured out how to generate predictors, so it uses a fixed set. If you want to try others to get better sounds, edit the source code, and if you create an algorithm to make them, great!
The source and program is free to distribute and use, as long as mention of the RWP and creators is done.
Have fun! Only some games use this format, so good luck. Most Rare games do. Hopefully source can also be of use to someone.
Note: Requres VS2008 Redistributable"