The nav system and empegability makes for very few choices. Acura's got a great nav system and the Acura TSX stereo has an aux input, to accomodate the empeg, or at least it did in the older ones. I don't know about the newer ones that have built-in XM radio. The Acura TL, though, has everything integrated together, so no easy empegization.

Subaru pisses me off. They've got the slot in the center stack where they install a nav system on the Japanese-market cars, but it's not an option on any of the U.S. models. Had it been there, I would have looked seriously at the Legacy GT.

In most new cars, though, you're going to have trouble with aftermarket stereos. Several manufacturers are offering different levels of iPod integration, which may or may not be good enough for you.