My 2006 A4 is all set to go for XM but I prefer Sirius. I just bought the car and originally had the Siruis receiver (dashmount) in my old car. My account is still active but I would really like to ditch the dashmount version. Can I get the XM receiver already installed in the Audi transfered to Sirius? From what it seems, I need to hook up with a factory converter. Is this true?
You'll need a receiver especially for Sirius. The XM module will only work for XM. You can put the XM module up for sale on this site or others to help pay for the Sirius one. You can find them on Audi sites and ebay from $180 - $400. The dealer will charge about $500. The install is easy (assuming it's in the trunk) as you just have to swap them out.
Hi! I bought a CPO '06 A4 about a year ago, and I had the same problem. It came with XM, and I wanted Sirius. The dealer said they would be happy to swap it for $450. I said I would think about it. I went online and found that the XM Module was in the trunk . I went on ebay and puchased a new Sirius module. It took about an hour (mostly to get to the XM Modules location in the trunk), but simply swapped the units out. Write down the units ESN before you install it (it can also be accessed from the radios display after its installed, but it is still handy to have it written down, so you can activate on-line if you want). Sirius even gave me three months free (because the OEM radio had never before been activated, they assumed it was a new vehicle! ). Also, in the end it was a free swap, since I sold the XM Module on ebay for a few dollars more than I had paid for the Sirius.
As long as you are fairly confident about opening some panels in your car, and you can unplug and plug in a few wiring harnesses, it really is as easy as just swapping them out!
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Sirius vs. XM - 
