Quick update.
I was able to find the pin layout of the connector X1880 which is the one behind the slip ring. Two pins (#2 and #4) are reserved to the paddle shift.
As you see both are indicated as "No signal processing in the control unit" which I interpreted as not used. As a matter of fact I checked and in my car and both pins are empty. This basically means that without some wiring the paddle shift will not work.
It may be hard to see but if you look careful you'll see pin #2 and pin #4 are empty:
I've also removed the connector X8532 that goes into the transmission mechatronic (identified as A7000a). As I said before our car sends a processed signal from the electronic Gear Selector Switch (S277a) to the A7000a through LIN-Bus connection on pin #8.
In other cars where the gear selector is a simple series of switches the signal for shift up/down (both from the gear selector itself and paddle shift) is sent through pin #4 and #5 respectively.
As expected in our car pins #4 and #5 are empty. Here's a picture of our X8532.
I'm still looking for the wiring diagram of an X6 with the ZF-6HP: hopefully that provides some additional clarity, but all I can say this far is that paddle shift on a X5 35d diesel won't work without some wiring...