Factory amp is feeding 2 ohm to each front channel. Door speakers are 2 ohm components. Amp is feeding 2 ohm x2 to each rear (woofer) which are dual coil. I.E. 2 ohm to each coil making the woofers 4 ohm each (2 x2 ohm).

You also have to watch out for the size of the cage and magnet on aftermarket speakers. I installed a set of JBL 2 ohm component speakers and had to trim the metal door mid speaker opening because of a slightly oversized cage and magnet. The Infinity components I installed in my other Xfire fit just fine with no modding.