I realize this thread has been dormant for some time, but it also seemed like the correct place to mention I've started work on reversing the Sound Blaster 16 DSP code posted here. Thanks to the forum members for posting the decrypted dumps, and Tube Time for getting things started with the SB 2.0 DSP. I've already found quite a few undocumented features so far. My main goal is to hit the 4.05, 4.11 and 4.13 firmwares available to see what's different.
Ultimately, I'd love to get my hands on the 4.16, but I imagine that would have to be dumped in a very different way given it's only ever found in a fully integrated solution.
Anyway, here's the work in progress. There's not much and only CTL files for a disassembler called D52 (which when combined with the CTL, will produce a source file that has labels and registers named)
https://github.com/SaxxonPike/sb-dsp-firmware
When I've completed this, I'm going to write up more on the undocumented registers, and perhaps also take a look at what that might mean for patches to DosBox. I'd also like to better understand the ASP-SB connection, but I currently lack a card that has ASP installed. (I used to have one, and traded it, oops.)