Audi CD Changer: CAN Messages from the Unit

Hello everyone,

I hope I'm in the right place; if not, please just delete this.
I have a question regarding CAN messages that a CD changer in a vehicle transmits.
My car is an A3 (manufactured in '07) with a Concert II+ (double DIN) head unit.
I had the vehicle's data bus lines installed in the glove compartment and installed an 'AudioLink' CD changer emulator. This device receives audio data via AUX-In from a Raspberry Pi. Now, I find it somewhat inconvenient to use a smartphone to control the playlists or skip tracks.

My question is (if it even exists) which CAN bus carries the messages for controlling the 'switcher' and what those messages are.
Does anyone happen to know the identifier and offset+length?

Since I've already found the TrackIdentifier, etc. on the Info-CAN, but there are no indications whatsoever regarding the hardkeys, I suspect that the control might not be handled via CAN.

Best regards and thank you in advance.
SkyRaVeR

CD changer CAN IDs must be encoded as x3x. For example, 0x130 or 0x037, although I don't know if these IDs are actually present on the bus.

Take a look at this.

http://www.canhack.de/en/viewtopic.php?t=2065