Audio Systems: 2001 olds radio harness, olds radio, wiring speakers

Question
i am planning to hook up an amp and sub to my factory stereo on a 2001 olds aleo. Gm is nortorious for having wiring brackets to fit into the back of their stereos. there are two brackets. one is being used by the factory wiring (speakers power etc...) there is a second slot for a harness. I am wondering can i plug a harness into there to send to the amp? or what is the second (smaller) harness slot for?
   thank you for your help.

Answer
Most times on a GM radio that extra plug is for an outboard player of some sort (ie. CD Changer, Cassette Deck)  There is no harness that you can plug in to give you an audio out for an amplifier.  Your best course of action would be to get a line output convert (aka hi/low converter) that would tap in to your speaker leads and gives you an RCA out to go to your amplifier.