Sounds as if prior owner added the Center console delete kit.
The options for installing a AVIC type GPS/Stereo is very doable as I and quite a few others have done before, search for AVIC and you will see quite a few with one member that sells the install kit for the double-din stereo.
Here is the link for install:
Recent Install - DVD Navigation
Maybe ask if car has the center console that was removed or look online at a dismantler or eBay as they are pretty easy to come by.