have you tryed flipping it over and seeing if it was upside down :shrug: if not the you will need to remove the headunit again and see if you can lower it somehow
 
i have an alpine 9857r, they have one mother of a white box which is attached to the back, making them a total bitch to fit!. i took mine to a specialist and he fitted it, the bottom tray ALMOST goes in all the way but it sticks out. way less than the one in the pic but still a teensy bit. if i was clever, i'd either buy a single DIN plate and sacrifice a shelf, or cut a hole in the back of the shelf for that damn box to sit in
 
Might have to try it the other way round then aimez, might give the cables a bit more room as well. It must just be one of those weeks, my xbox 360 died again last night and ive only had it back since last Monday!