You probably want to start with the concept of MIDI Learning in the Zynthian world.
https://wiki.zynthian.org/index.php/Zynthian_UI_User_Guide_-_V1/V4#MIDI-learning_.2F_binding
This allows you to intelligently map external MIDI controllers to parameters within the individual chains which can frequently get you going without having to load any form of specific driver. But, switches on full sales pitch voice) if you do want to write a driver, you now can !!!