Audio Systems: VW Ipod Adaptor...was I mislead?, vw passat, ipod interfaces

Question
I just bought a new 2006 VW Passat with Navigation and 6 disk changer in the glove box. I was told that  VW makes an Ipod Adaptor that when installed will let me control my ipod through my nav screen....awesome....NOT REALLY. I was todl today by the service guy at the local VW dealer that if he installs this, i would no longer be able to use my navigation...its one or the other since there is only one jack behind the radio. he also said he has only put one of these in and it didnt have nav. Do you know this to be true? if so, is there a Y splitter that would let me use both?
Thanks

Answer
i have install a couple of the ipod adaptors my self but i never seen a car with the nav system.
  what i run in to was vehicles with the cd changer in the trunk and console and both times i have to unplug the cd changer  because teh ipop takes the port of the cd changer
and the radio believes the ipod is the cd changer you can not have both  about nav system  i am not sure please call
407-933-1065 ask for andy he knows a lot about volkswagens  and they make the ipod interfaces