Welcome to the forums. Theres lots of information here in previous posts, and it makes it fast to find stuff by using the search feature, as most questions have been answered sometime in the past.
anyways, so you want to be able to switch the amps input between the headunit and computer? or do you want to replace the headunit with the computer?
im not quite sure the best way, but im trying to clear things up so someone else can answer the question easier.