The A4 is not conveniently designed for a Sirius radio. I say on audi diy that there's a part you can get to plug it into the factory stereo: 8E0 035 593/8E0 057 593 Sirius without RNS-E and without tire pressure monitoring system. Problem is I can't seem to find anywhere that sells the product. Does anyone have any experience with this part and maybe some insight on where to buy it? A4 03 B6..