Okay, so the NDS isn't natively a DAP, but it has decent potential to act as one.
For the last year, NDS homebrewers have achieved quite a number of remarkable feats creating homebrew apps for the ds, including several ones that would let your NDS act as a DAP, with full support for several audio formats, (running software codecs on the ARM9 core in the DS) and with excellent performance.
In fact, i'm running a 192kbps mp3 on mine right now, performance is great.
Yet i miss the greatness and adaptivity that rockbox brings.
NDS hardware has allready been mapped by the DS homebrewers, and libraries have allready been built to address most of the hardware the DS sports.
A porting effort might thus be relatively easily executed.
I'm a relative newbie to programming and compiling C (have only had experience with java) but i'm looking into DS homebrewing myself.
I will investigate the portability of rockbox as best i can, but a little help wouldn't hurt