IIRC, the Shaker 500 door subwoofers are dual voice coil subs and have an impedance of 1.2 ohms each. Sadly, you have right at 3 inches of mounting depth in the door, and even then you are pushing it at certain parts and will need a heat gun to reform the plastic. Even
**THESE** subs will require that you reform the door pods, and they have a lot less mounting depth than the Kickers you mentioned.
A while back I emailed with an installer and he told me that he installed some 8" infinite baffle subwoofers to replace a customer's Shaker 500 setup. He said that he removed the sealed door pods, deadened the doors, and added some lead to mass load the plastic door panel. He also used a layer of foam to decouple the plastic piece from the sheet metal in the door.
As for the amplifiers, I highly doubt they provide much more than 50 to 75 RMS to each door subwoofer, so you may want to look into a more powerful amp if you replace the Shaker 500 subwoofers. I was also told the stock amplifiers could be bridged, but no one ever told me how to do it. Furthermore, the Ford dealership told me it could NOT be done so that leads me to believe the Shaker 500 amplifiers are somewhat limited.
Shaker500 questions 
