There was some discussion about pitch detection here
Regarding quadraphonic audio, FAUST has some relevant functions that I’ve ran on Daisy Patch with OWL successfully. Things like panner, mixer and a suitable reverb (4 channels from an FDN reverb). They tend to be a bit more computationally expensive than I’ve expected out of the box, so using C++ might be required if you want to have more than 2 running at once.