Just a heads up for anyone else who comes across this issue when installing an aftermarket stereo into a Crossfire that had a factory navigation unit: I went down to a car audio place (Audio Lab in Lake Forest for those of you in Orange County), and they gave me a Raptor AD-VW1 antenna adapter. It fit perfectly and my new head unit works great.

I Googled the adapter and it looks like it might be discontinued, but I thought I'd throw the information out there in case someone searches for this issue in the future.