The easy answer is it wont know. You'll have to design a circuit to handle it automatically. Instead, you can use the line-in on your PC. Connect that to your radio and centrafuse will control it automatically.
If your computer doesnt have a line-in (blue audio port), then you can check with mitchjs on the board and see if he has any usb line-ins left, or buy a cheap external soundcard with line-in support.