Alpine has a piece to adapt a ai-net changer cable to a usb storage device.

You can see the 5 gig sony device in my glove. The box was plug & play. No power wires required & the piece cost $110-$180. It works just like a changer but better & cheaper

Alpine does not have much info yet but here it the link to my setup & the product

http://forums.nasioc.com/forums/showthread.php?t=1138069&page=2

http://www.alpine-usa.com/en/products/product.php?model=KCA-620M

Kenwood KDC-X590 has USB input on the headunit and the whole thing is only slightly more than that add on. I guess if you really need features that are provided by the high end alpine or if you're an Alpine fanboi it would be cool. If you're just looking for a decent head unit with a moderate set of features and some USB input there are much better options IMO. Still looks nice though and very good job on the screen install.