I'm looking at getting the Dension 500 for my car, been reading alot about it latley. For the owners of them, what is the max hard drive size I could hook up to one? I'm assuming it would have to be USB powered, or does anyone have a 3.5" external hard wired to power? I got a couple extra 3TB externals, one of which I'd like to dedicate to just having in the car hooked up to the dension.