Wow, huge news. There is finally, after all these years, an awesome free and open source audio playing library for the Nintendo DS and GBA. Hooray! This is big news for me as Looper Advance has been built against the non-Free Krawall library for years now and it's always irked me, quite appart from making the GPL license on Looper Advance invalid, and probably illegal.
Hopefully I'll get a chance to update Looper Advance soon and then I can release it properly as 100% Free Software.
MaxMod appears to be pretty comprehensive in that its API provides for mod-playing, sample-playing, and direct access to streaming buffers. This basically means you can write apps which mix and match all three types of audio playback.