Hrm... Thinking about it, I think I may end up just going with tearing out the head-unit and putting in the empeg with a 4 channel amp. Since the head unit can do line out, I can always move them back if I find it's not what I want. Means I get to upgrade to an amped system though..

I posted a few pics here, lemme know what you think (The tray slot has about an 8 inch depth to it). Personally, I would hate to be in the backseat if the empeg is in the tray location, as you wouldn't be able to see the display.