The wiring harness is likely going to be different. You can look up the wiring harness for the two different audio system and it will show you outlines of the connectors and the wiring, so you can compare the two. NICO Club's site has free, online FSM's at their site.
Update. I got the new radio with the 6 disc cd changer. I got it installed and it went in without a hitch. Fit perfect and all the connections went in. Now the new one has a extra connection that my old one didnt but everything works so not sure what its for. A friend of mine said it could be for a equalizer.