Where is the factory amp located and how much power is it supplying. I have a 97 lariat with the premium sound system. Cass/CD HU, 6 disc changer.

I just replaced the factory Front Door speakers with 220w pioneer 6x8s. (RMS is 60w). I'm planning on replacing the rear set with the same speakers.

Some say the premium system has a factory amp, can I add another amp or is this going to put out enough.

Thanks in advance