Ext disp means external display ---> connection to the info display (may be optional)
ext amp means external amplifier---> connection to an amplifier , in your case optional since there are no wires in it
for cd is correct , it goes to the cd player
as for your carpc , I dont know if your radio has an audio in port , if it does it will be a lot easier.
and if you are going to use a carpc , wouldnt it be easier to let the phone connect to the carpc , that way you wont have to switch devices on your radio