DSP 'generally' is only an issue for 2002 or earlier cars, they have a Digital audio input from the CD Changer so you need an A-D converter if you want to use any of the CD Changer replacement interfaces. There are some newer cars that have digital DSP, the only way to be sure it to look at the connections to your CD Changer, if you have a small coaxial cable disconnect it and see if you still get audio. If you do get audio or don't have the coaxial cable at all, you don't need the A-D converter.

You should check out the Intravee as you have Nav.