This unit doesn't go in through the antenna though so sound quality should be more than fine. I have the Mopar iPod Integration Unit in my PT Cruiser (similar sort of adapter) and the sound quality is excellent. I'd love to know for sure if this thing works with our NAV units. I've not pulled my radio out to see the backside, but if it has a connection to accept this adapter (FP, are you reading???????????) then odds are we should be good to go.

I believe what you're thinking of is the units that essentially splice into the antenna inputs - those will have the same limitations as a radio broadcast (frequency response, dynamic range, etc) so they'll sound better than a wireless transmitter only because there won't be any static as the unit fights with regular broadcasts. All the splice-into-the-antenna units I've seen basically kill the antenna inputs when using the iPod.