Are they maxxed out by the factory amp?

Also would a crossover allow me to make my 6 X 9s control the bass?

It is an extreme challange to replace the factory amp for several reasons... 1) The factory speakers are 2 Ohms, most after markets are 4 Ohms. Aftermarket amps are generally designed to run best with 4 Ohm speakers and anything less can damage the sound quality. 2) Worse yet, the way the factory amp hooks up is completely incompatible with how aftermarket ones hook up. I'm not really sure what Chevy did, but you really should get some Hi to Lo voltage converters (takes the speaker wire from the back of the deck and converts it to RCA's which is what you need to hook up a new amp). You'll find adding an amp and new front and rear speakers to your factory radio can you give some absolutely great sound.