Here's the deal, Changer capable headunit can control IPOD with corect adaptor, ie something like the model you posted, or ICruz (http://www.monstercable.com/icruze/) by Monster...
Changer capable headunit with factory changer, no IPOD control from headunit...
If the changer is connected to the factory deck, the buttons are already being utilized and won't control the ipod. In your case, the buttons are being used, so this unit will not work for you... You can, however, run an aux adaptor like the soundgate model to run IPOD input into the headunit via hardwired FM modulator, but the IPOD is still the control piece.
Thanks ROZ for the info. I guess that I'm S.O.L.