excellent, i'm willing to learn swift or obj-C for this, are they API-equal?

(actually i don't know much about M4L, supercollider or those others, but i do have a bunch of HW synths: kurzweil, DSmith, emu, kawai etc

Either one is fine for AudioKit. Swift is still evolving a bit, might want to stick to Objective-C if you're learning.