well, it didnt take me too long. on top of everything that has been reasearched i made a minor discovery that i though should be listed.
ok, the ds sseq file that is responsible for sound contains 3 types as you already know. that is the sseq, or sequence (aka midi) the sbk or soundbank, originaly though to be a soundfont like clone, and the sample files in a wave like format.
the basic understanding when working with midi is it usualy uses a general standard called respectivly, gm or general midi. the gba followed this standard with very strict exceptions. the ds, however, followas a varied standard.
ok, time to slow down. we need an example. ok, lets say, the pokemon trainer midi file has a gm instrument of a flute, as does the rival. in gm, it always plays the sample associated with the flute. but on the ds, the soundbank controles what sample is to be played. so you may have these 2 songs containg the flute in it, but they may play a trumpet sound. why is that? the soundbank tells the ds the samples to load. so one song may play a trumpet, one may play the sax, and the 3rd my play the clarinet, even though they may all be listed as a flute. that why ds rips sound less like their counterparts on the ds, and why you can have 3 channels for drums, even though the gm channel for drums is channel 10 only. i hope this continues to make the research clearer. feel free to ask any question and i will try my best to answer it.