i have always been under the impression the the reason why we couldnt get a top notch snes emu on the ds (or the gba) for that matter has always been the audio problem. I am pretty sure the snes games have 16 tracks of audio that to work on the DS/GBA have to be down converted to 2 tracks stereo.
the psp however has 16 track audio, so it was easier.
there are also some games like star fox and chrono trigger that have an extra chip in the actual game that is hard to emulate.
the psp however has 16 track audio, so it was easier.
there are also some games like star fox and chrono trigger that have an extra chip in the actual game that is hard to emulate.

