Installing subs on my 9-5
 

So I want to install a 12" in my car and keep the factory speakers because I think they are sufficient. I am buying a head unit, wiring, subwoofer, and amp. Now I was just wondering if there is a possible way to keep using the factory amp that currently is powering all the speakers and have the new amp I'm buying to only power the sub. I need to know if I can disconnect the amp from the factory head unit and reconnect it to the after-market one.