Great writeup and summary. Here are some other points that I've come up with in the past few weeks since I've become a Crossfire owner and been researching info about this.

- The Factory Amp (located under the floor at the front of the Passenger side) contains components and wiring that don't appear to be related to the stereo, so you cannot simply replace the factory amp with an aftermarket amp. The system schematic shows wires for "Body control module" and "Controller Antilock Brake" going into the factory amp.

- The Rear speakers appear to be 6 3/4" dual voice coil subwoofers. I haven't seen any specs on them, but some posts here suggest that each coil is 2 ohms and the factory amp provides 35 watts per coil (70 watts per subwoofer). With an aftermarket amp, you can wire each coil in series for a 4 ohm load, or supply each 2 ohm coil with a powered channel from the amp like the factory system does.

- The factory amp is pretty expensive. I haven't been able to find any on eBay, and a new one is close to $500 from a dealer. It is actually a 6 channel amp. Each side has a channel for the front door speakers, and then 2 channels for each of the voice coils in the rear subwoofer for that side.

I'm troubleshooting a problem with my new 2005 limited roadster. I get no audio to the right side (either door or rear speaker). I've verified that the factory head unit is outputting DC on the right side, and that probably means that the right channels on the factory amp are fried as well (although I haven't been able to verify this yet). So I'm trying to come up with the most cost effective solution to replacing my head unit, likely needing to bypass the factory amp because it is fried, and keeping the front and rear factory speakers to keep costs down. It seems that sending only 18 - 25 Watts to both coils in those back speakers from the rear channels of a new head unit would be significantly underpowered compared to the 35 Watts each coil is receiving from the factory amp. So that would mean adding an after market 2 or 4 channel amp, which I know nothing about installing and would add more cost into getting my system working properly.