A -ton-
No hesitation to enthusiastically share that it was actually a parallel goal to see just how deeply I could go while keeping it stable, performant, and extensible for the long term.
I ended up building a lot of ancillary agent infrastructure to push the determinism in all the fanned out work slices, too.
Did you give any thought to using JUCE as a general framework? This way you could add more synths very easily ..
(Apologies if you already do, haven't looked for sources yet..)