Here’s a really interesting article on the Jalopy Journal with some good information about hooking up an iPod to a hidden amplifier. The interesting part is the iPod dock connector, which I’d never really thought about searching for before. I believe the Kenwood head unit I have is equipped with RCA jacks that will support AUX input, so I may switch over to that instead of a mini stereo cable out the front.
Update: I’m out of luck with the Kenwood unit (it’s got no aux inputs on the back), so I may just sell it on Craigslist. I never liked the control/button setup anyway.