I have changed out all of my doors with Alpine SPS - 17C2 6.5" 2 WAY SPEAKERS 250W. I still used the factor amp which is doing an oustanding job in conjunction with the head unit. The main difference is that I have also upgraded my head unit to the Ecplise AVN 5495
The trick is when you go to remove the old door speakers from the doors, you have to press out the old speaker with you hand (they are held in by strong glue/slicone). You will start to notice the speaker moving slowly away from the plastic housing that it is enclosed in. once you have removed the speaker from the housing simply insert the new 6.5" speakers (which will fit perfect), screw them down in the housing and connect in the wires. From this point re-install the housing back into the door, do a test and you should be ready to go.