I already posted this over on the devkitpro forums, but figured it might just as well be welcome here.
Anyway, I have ported our original PC-based musicdisk to the NDS. The musicdisk features 26 songs in a mixture of streaming (.ogg) and various module (.mod/.xm) formats, with nifty visualizers running at a full 60fps. Sound quality is extremely good when using headphones or earphones (the internal speakers are OK, but not great).
I didn't use maxmod as I have my own replay code, and I had to make some custom additions to the ARM7 side, but we finally got it done. Next year we'll try to do a simultaneous PC/NDS release.
Thanks goes to WinterMute and the libnds team for providing the low-level libraries and a libtremor port that worked flawlessly the first time! \o/