I can't see anything obviously wrong with it, I'm curious about why it has so many connections between the audio board and the Teensy, also your note handling routine isn't that great which might be causing it to crash, really you need a better...
I tend to agree a sync function is missing from the oscillators. Would be nice to have.
This synth although it's turned out well was more of an experiment than anything else, it gave me an opportunity to use the audio library, maybe not...