I'd be happy to share any knowledge I can on GameCube audio. I've recently put together a GC-DSPADPCM decoder and encoder that actually works pretty well in multiple games.
https://github.com/jackoalan/audacity/releases
To demystify the DSP format somewhat, it's a proprietary flavor of ADPCM; Each sample is iteratively "predicted" based on the last 2 samples and a set of 8 coefficient pairs (which appear as 16x 16-bit values, or 32-bytes in the file header). The encoder bears the brunt of the complexity, using a discrete-fourier-transform to analyze the audio in the frequency-domain; selecting coefficients with the least error.
If the game in question truly uses MusyX, the SFX are likely bundled in resources known as "sound groups". Metroid Prime 1 and 2 both use MusyX and sound groups for the vast majority of SFX. MrSinistar from M2K2 and myself have reverse-engineered the majority of the sound group format (designated "AGSC" by Retro).
http://www.metroid2002.com/retromodding/wiki/AGSC_(File_Format)
In particular, check out the Pool, Proj, Sample, and SampleDirectory sections. These are the 4 main "chunks" of a MusyX sound group. Different games may arrange them in different orders (in fact, MP1/2 swapped locations of Sample and SampleDirectory), but if you can identify the signature layout of MusyX in a hex-editor, i may be able to modify my "AGSC Extract" tool to help out.
https://github.com/jackoalan/agsc_extract
https://github.com/jackoalan/audacity/releases
To demystify the DSP format somewhat, it's a proprietary flavor of ADPCM; Each sample is iteratively "predicted" based on the last 2 samples and a set of 8 coefficient pairs (which appear as 16x 16-bit values, or 32-bytes in the file header). The encoder bears the brunt of the complexity, using a discrete-fourier-transform to analyze the audio in the frequency-domain; selecting coefficients with the least error.
If the game in question truly uses MusyX, the SFX are likely bundled in resources known as "sound groups". Metroid Prime 1 and 2 both use MusyX and sound groups for the vast majority of SFX. MrSinistar from M2K2 and myself have reverse-engineered the majority of the sound group format (designated "AGSC" by Retro).
http://www.metroid2002.com/retromodding/wiki/AGSC_(File_Format)
In particular, check out the Pool, Proj, Sample, and SampleDirectory sections. These are the 4 main "chunks" of a MusyX sound group. Different games may arrange them in different orders (in fact, MP1/2 swapped locations of Sample and SampleDirectory), but if you can identify the signature layout of MusyX in a hex-editor, i may be able to modify my "AGSC Extract" tool to help out.
https://github.com/jackoalan/agsc_extract