I have a 2001 BMW M3 and I am getting an SIRIUS XM radio for X-mas. I just found out that the model does not come with a built in FM transmitter (SIRIUS Sportster 5). Is there any other way to connect it to this car stereo, or do I have to buy a FM transmitter with it? I dont belive I have an audio input on the stereo, unless its hidden.