I checked with Audi Genuine Parts and they are selling a brand new Sirius brand receiver for $543. (MSRP $767.03)
I bought this XM brand receiver used on ebay for $49.95.

XM Satellite Radio receivers have two antenna inputs, one Leaf Green FAKRA-E Male input for Satellite antenna and one Nut Brown FAKRA-F Male input for XM terrestrial signal antenna.

This XM Brand Satellite receiver was offered on the 2006-2007 A3 models and only Sirius Brand receivers 8E0 035 563 Q were offered on 2008-2013 A3 models.