I just put one in mine. Invisible and is the same one as the Allroad with the vertical receiver. I purchased it from allroadhitch@gmail.com. The RS6 doesn't have the factory wiring harness for the hitch so a trip to a auto parts store is all that is needed. Here is a link to an RS6 with this hitch. Not my car but rather pics provided by the manufacturer of the hitch.
https://www.dropbox.com/sc/dvc8m7spc...Vks_5WhdOmma#/