I just purchased an 06 A4 S-line and I am not sure which radio system I have because this is my first Audi. I know its OEM but I believe there were different choices. It doesnt have a CD-changer or Nav and it does have a CD and Cassette player. I would like to install an I-pod interface and noticed there are several on the market. Is any one system the end all best one or are they all pretty similar? I would appreciate to hear from people on their experiences with doing this.

Thanks,
Bob