My suggestion would be to ditch the factory Nav. Aftermarket is more accurate and much less cumbersome and not only that but when you swap out the deck it will make your system sound that much better.

As for the people looking for iPod integration into the OEM head, I have two suggestions. IceLink is one. I work at Tweeter and this is one of the application we use when trying to integrate iPods into factory head units. It's also one of the few things that you can actually connect to our systems. We're limited by the DSP chip for our sound systems, essentially making it damn near impossible to do anything with it (got to love luxury car systems...) and it does have a few big limitations and some have found out. The second way (and my preferred way) is get this unit made by Alpine called the Vehicle Hub Pro. Basically what it is, is a hub to connect aftermarket components (I.E. an iPod) to your factory head unit. It does cost a pretty penny, $500 or so, but the expansion capability is what makes it worth the dough. If you want to check out more details about it go to Alpine's website: www.alpine-usa.com.