SFX ripping/decoding/dumping features?

[mbc07]

Well, one thing is certainly: the sound files must be in an format handled by GameCube's DSP, and almost all formats handled by GameCube are handled by VGMStream plugin too. Since you didn't find them in a "play-ready" format, they're probably packed/encrypted in some kind of container or package in some file from the ISO. You could try finding that file in the ISO and then asking for help in XeNTaX forums. They have a forum section dedicated especially for finding tools to decode/decrypt a lot of game file formats...