I've tried a few of the FM transmitters. The Transpod from DLO (http://www.dlodirect.com/ and discount online retailers such as amazon) has a strong transmitter and a nice way of holding and charging the ipod.

However, I got the PIE converter FRDW/PC-POD (http://www.pie.net/applepie.cfm) as soon as it was determined that it will work with the internal GPS system and 6 disc external changer. I don't know which PIE product, if any, will work with your system, but PIE has a very responsive customer service telephone operation and they will try to help if you call.

By the way, I also loaded the latest Potter book on my iPod, but found that some chapters skipped or had other audio problems. The discs were fine; something got screwed up in the transfer. So now I'm back to listening to the discs. If you're going on a long trip, bring the discs with you, just in case.