How powerful is the audio? a 30A fuse sounds small. For the amps to connect to the carputer, id recommend a USB sound card such as the Sound Blaster Audigy NX.
Frys, Wal-mart (and perhaps Target) carry distribution block. So do all car stereo shops.
The Xenarc can be connected to either the car pcs powersupply on the 12v line, or thru a dc-dc regulator to the cars electrical system (or directly to it if it has a regulator in it, not sure)
A usb cd/dvd drive will allow for a more flexible installation. They have ide (or laptop) ide to usb converters.