I followed this design made by someone else.
Then for the audio:
The points to solder to on the board are marked out in this picture, which I also found elsewhere. 2600 chroma was labelled incorrectly though so I modified that (white arrow). The white wire is 5v (which you'll also need to know). A lot of the pictures I found about this mod were for different models/region. The only one that matched mine, which is a PAL-I system was this picture.
The audio bit is descibed here (scroll down a bit).
Index | Mods