I used a Blitzsafe (
www.blitzsafe.com) adaptor that goes between the interface of my changer and the line running to the head unit. I tune the cd to channel 99 and play XM or my ipod and the sound is very good, as good as my cd's. Prior to this, I used a cassette adaptor, but it was marginal. It was a bit complicated on my X5 because it has navigation, but for other cars its easier. On my wifes car, I used a direct fm interface that really work pretty good. I still think your freq response is limited compared to cd's but for XM it worked well. Fm and cassettes are last resorts in my opinion, especially with the quality of iPods.