Audio Systems: 98 Passat Subwoofer Install, rear pillar, rear deck

Question
Hi there,
I have a 98 passat that has a cd changer in the trunk with the factory deck and I was wondering what the best way to add an amp and a subwoofer was without screwing up any of the wiring already present. Ie.. what's the best way to get the signal to the amp and what about the 12V turn on signal? Any help would be greatly appreciated. Thanks in advance.  

Answer
if you have the moonsson system all the wires areon the rear pillar by the door or  rear deck  you can get the wires from the factory amplifier

if you have the regular sound system pull the radio and the the outputs and remote from there
you will need a hi/low interface