Awesome work! I love the care and attention that people put into understanding these devices.
I'm currently in the middle of a vintage synthesiser hacking project as well. Last year I made a fully annotated disassembly of the Yamaha DX7 firmware, and did some other technical analysis of the synth. Since then, I've been waiting for a chance to put this knowledge to good use. I found a DX9 on a local trading site, and I'm in the process of hacking its firmware to remove the 4-operator restriction that made it such an unpopular synth.
I browsed through the repository as discovered by colejohnson66 downthread https://github.com/ajxs/yamaha_dx7_rom_disassembly. This is an example of superb, meticulous, lovingly documented work. The kind of thing you don't see every day, congratulations. The attention to detail is really just chef's kiss, starting with a really good repository name (a small thing, but still), continuing through clear and apparently comprehensive documentation of what you did and why, then on to beautifully formatted and commented assembly language (much better than the original source code I'd wager) with coherent and consistent paragraph commenting a particular delight, and finally (and very importantly) dedication to making sure others can reproduce your results and generate a matching binary too. There are likely to be other things of beauty in there I have forgotten to highlight, it's just that good. Oh the FAQ of course, what a great FAQ. Really I am being very wordy for someone that's lost for words.
BTW, I love retro computing too, this is my best attempt so far in the field https://github.com/billforsternz/retro-sargon. I aspire to similar standards to your good self, but I'm not there yet.