Double DIN means it's twice the height of the common head units you see in the shops etc. so the face is not so much like a rectangle shape but closer to square - like two normal head units sitting on top of each other. - All AU2/3 head units were double DIN AFAIK and I believe there was at least one single DIN ('regular' size) in the AU1 range.
According to the manual, as well as to my knowledge, every AU2/3 head unit had at least a single CD player, so it's sounds like yours must be from an AU1 maybe.
Also, the main plug on the AU2/3 is different according to the manual, with only 8 pins on top. I will give you the pinouts anyway for the AU2/3, connector 186 (which is the main one and is common on all the head units in the range). Just keep in mind, it sounds like yours is a different unit so this may mean nothing to you (ie. don't assume yours will be the same or similar to this), but it's all I got - may proove of use at some point:
I am listing the function of each pin, one after the other and when you are looking at the back of the head unit holding it the right way up - I will do the top row first and then the bottom row - from left to right: