I'm looking at adding a Dension Gateway 100 (or 300) to the 'Concert' head-unit in my '02 A4 Avant. Could I do this myself? It seems to be as straightforward as one plug into the 20-pin ISO socket (or have I missed something....??) I'll need to buy radio keys to extract the head-unit, but I don't know what I'll see once the unit is popped out, and I've never done this before! If it is as simple as plugging the Gatway into the back of the head-unit, will I need to anything power-wise (disconnect the battery etc..) I'm not frightened to give this a go, but any tips or advice would be appreciated!!