I'm not an expert, but I would think it is all one unit. If that's the case, and I am willing to bet it is, you are stuck with it unless you want to install a new stereo/navigation unit.
There are some really good ones out there starting at less than $1,000.
Pioneer-> DVD / Navi / MP3, it actually plays everything. Has a dozen color settings so I can match with my instrument cluster. Works inconjunction with the AUX / iPhone port in the center console (has a jack on the face as well). On top of the features it sounds a ton better.
I don't think that is what he was asking. I think he wants to use the factory navigation but change the audio portion.
I am 99.99999 percent certain there is no way to do that.
And if there were, it would probably be cheaper to change out the navigation unit too.
so i'm assuming he wants to add an aftermarket amp and sub woofers for more sound? I'm kinda in the same boat as mine also came with navi from teh factory so hopefully somebody will chime in.