As being an owner of 206 1.6XS (May 2002), your request is also on my ToDo-list. My car also has such control (SRC control is a rotary button in middle) in combination with complete integrated Radio/CD player. As far I've seen, the control and displaying are over 2 wires (and the GND). The most interesting part will be interfacing with the display, which is (I hope) feasible to do since the build-in radio is a quite standard OEM-factory radio. So lets hope we've no interfacing to that digital bus / multiplexed wiring.

And where is my Empeg in this story?
Well...
I planned to put my empeg in the place of the factory radio when I've all information to integrate it with control+display. At that moment the radio moves to dashboard locker (where my Empeg is running now......don't hit me...)

Keep you in contact when I've made progress (but at the moment busy....very busy).

Cheers