You might want to look for a car audio forum dedicated to just audio. This whole website is about car computers and this small section is about integrating the car PC with the audio part. Sticky right at the top of the page of this very subforum:
http://www.mp3car.com/vbulletin/car-...questions.html
IMO, the amount of power you have does not necessitate the use of a cap, and the extra batteries are good if you plan on jamming with car off but will put more strain on your alternator while the car is running. I've got over 2000Wrms divided up across my entire setup and I don't use caps or extra batteries.