I don't remember completely, but I feel like I read that Donkey Konga uses a stereo variant of DSPADPCM (usually .dsp files are mono). It's possible they made a little custom tool for making them and never released it as part of the SDK. I think https://hcs64.com/vgm_ripping.html has what you're looking for if you want to convert them back to .wav.
Also I'm not totally sure, but you're probably going to get banned for admitting to pirating the Wii SDK, so good luck with that.
Also I'm not totally sure, but you're probably going to get banned for admitting to pirating the Wii SDK, so good luck with that.