My KJ came with the stock AM/FM single CD player.
It is probably the best sounding factory radio I've ever had.
I'm not really that interested in replacing it, but I do want AUX in for my iPod.

My head unit has cd changer controls, so there's a way in.

Removal instructions for the factory rig

Aux In Options

USA Spec aux in interface. Provides two aux in inputs via the cd changer interface.
$60.
Periphial ipod adapter. CD interface, allows control of ipod via cd changer controls. $200
USA spec ipod adapter via CD if. Looks nice, $120.
Harmon Kardon Drive + Play
Very cool, essentially a complete player minus storage/playlists which it uses the ipod for.
Syncing a car computer off an ipod would give the same functionality, really.