I have the accord coupe with navigation. I want to install after market stuff in the car. I kind of ran into a problem.

I want to get an mp3 head unit installed, which the accord has a spot for. When i went to a place to see how much it would cost for all my audio system to be installed the guy told me he cannot install the head unit because it would knock out the audio system in the navigation screen. I guess that made sense BUT i also know as an accessory honda offers a mp3 player. I'm thinking how can they add this mp3 without messing up the navigation... Isn't possible to install a head unit in the accord without disabling the navigation system?

I'm thinking that in this spare spot they'll be some type of wire harness un-used since i did not get the extra option through honda.

Hard to type into words what i'm trying to ask. If any of you understand what i'm trying to find out please help!

Simpliest form of question, Is it possible to install an after-market head unit without messing with the navigation settings?? Will the regular radio, xm radio and original radio still work?

Thanks!