Just run audio from the laptop to your headunit. If the sound quality is unacceptable, then look into a USB sound card. Remember that a USB sound card will suck away CPU cycles.I would get an external DVD writer through USB and the usual.
For sound to the car speakers, would it be best to use an external sound card? I have two 4x4s and two 6x9s in the truck that I would prefer to use, and the head unit I have will find its way to another vehicle.
Easiest would be the car power adapter for this model.Also, what would be the best way to power this from the vehicles battery?
It's time to read the FAQs.