http://www.zophar.net/utilities/spc.html has a bunch of converters, particularly a MIDI converter - midi playing is one of the easiest things to code for the GP32.
I odnt do it much, as Im not good a creating stuff that sounds decent, but if anyone wants me to try and do anything for them, give me an IM or somehting, and when I get round to it (it should motivate me!) I'll write some stuff, for an app or a game, I dont mind