That'll be the same page where they read about that "we'll put line inputs on it, but we'll authenticate against our own brand of in-trunk CD player only, and only turn the line inputs on if it's present" crap.

Yeah, but many such animals (Kenwood HU's in my experience, and others I've seen advertised on Crutchfield) have a cable that they'll happily charge you an arm and a leg for, which can convert said line inputs into all-purpose line inputs suitable for connecting to, say, an empeg car player. You know, because they're accomodating like that.