[elihu]

Haken Continuum, perhaps?

The same Eaganmatrix engine used in the Continuum has also shown up in the Expressive E Osmose, so apparently Haken is willing to work with other companies to integrate their synth in more products -- and the result is quite an amazing device. Haken also makes a standalone Eurorack module.

I'm not sure if there's a good open-source MPE synth that's easy to port to microcontrollers. Surge is really impressive but it's not made to run on simple embedded platforms.