For people wanting to help with it, here is SDK 1.4.0a1 with preliminary DSF support. THIS IS NOT FOR END-USERS AND YOUR EARS WILL BLEED IF YOU TRY AND PLAY ANYTHING WITH THIS!

The AICA is there as a baseline. Registers, timers, IRQs, envelopes, and 8 and 16 bit samples work, all adapted from the current SCSP. I tried to port ADPCM from Chankast's AICA (which was forked from MAME's SCSP 2 years ago) but it's not working properly. The DSP's disabled at the moment, and the filter and filter envelope are not present.