Has anyone used this unit? I want to use it in to my 1996 C220 with stock head unit. Can this be plugged directly into the back of the head unit or does it have to plug into the CD changer cable in the trunk? I want to put the iPod in the smaller compartment under the arm rest. Where is the best place to put the interface? Will it fit behind the head unit? How difficult would it be to run the cable from the interface to the iPod?