There are CAN2USB adapters and the Audi Infotainment CAN is using common 100kbits speed. But figuring out the 2 way communication between the head unit and the SAT receiver could be a little tricky. You would first need a PC and CAN2USB or CAn2COM adapter and log the traffic between the head unit and SAT receiver to get an understanding on how the communication looks like. Ideally you would do this outside the car, with only the head unit, SAT receiver and PC connected to the mini CAN, otherwise you have much to much traffic to decipher the messages. Once you know how the messages look like you could write a PC application that emulates the head unit and talks to the OEM SAT receiver. Overall, not impossible but pretty time consuming because you have to reverse engineer everything on your own.