Sorry i misread what you wanted to do.
If your wanting just going to try to find a stock nav let's say out of a wrecked GXP or so then you wouldn't need those modules. However you would have to take the car down to the dealer for them to unlock the radio and won't require the modules I was suggesting. The stock navs don't pop up to often and usually when they do they sell for $800+ or so and then you have to make sure it's complete (includes nav cd, antenna etc)
If you wanted to go with a aftermarket head unit that had nav or so you would need to purchase a GM0S-04 harness that allows the door chimes and onstar to keep working. Without it, it usually will flashes security warnings. Now if you also wanted to keep lets say your steering wheel controls you would purchase a steering wheel module for whatever brand of headunit you want (ex: if you buy a alpine headunit you'll buy a steering wheel module for alpine headunit)
Let me know if I made sense
