Does anyone make a car adapter for a microsoft Zune that doesnt use an fm transmitter?

I live in a metropolitan area with many radio stations. So, i get quite a bit of interference........I have tried 2 different types of fm transmitters, and neither work very well. Both have static. I would like to find a auxilary adapter for the stereo-a Rockford Fosgate 6 disk changer-in a Nissan xterra (stock head unit).