Wow First reply on 3 newbie questions in one 10 minute session.
Although they arent asking to be spoonfed too much.(this guy is a little, but oh well)
You could buy a new amp......
or find out which pins on your bose amp are the inputs and make a harness
Probably be a pain in the arse
Also you might wanna try and findout what the input voltage is on the bose amp and compare what your soundcards output is.
Good place to find information is forums dedicated to your car. www.nissanforums.com