fantastic, thank you!
Will it be apparent where to wire in the radio to this and then the 9 wire to it? or is there a writeup somewhere that I can't find on the Google Machine?
i think that it is apparent, but i also did this for a living for quite a few years. Google will almost certainly have this answers for you as well but ill give a summary of how the wiring should be done.
from the radio connect RCA cables to the 4 channel amp. This is your low level signal into the amplifier (if your amp supports high level input you can do that too if you like, that is up to you and there are good and bad reasons for both options)
From the 4 channel amp to the harness, connect speed wire to each of the 8 outputs on the amp, run the wire up to the radio cavity, and connect it to the color coded speaker wires that plug into 1 of the 2 ports shown in the picture above. Alternately you can omit that harness all together and hardwire the speed wire into the factory wiring, but running through the pac module should be fine unless your are exceeding 50 watts per speaker, which if memory serves is all the module is rated to pass through it. If you are exceeding that you need to hardware the speed wire into the factory speaker wires behind the radio.
You need to run the blue/white wire from the radio to the amp, there is a blue wire in the 9 wire that is intended for this, connect the blue/white at the radio to the blue wire in the speed wire, and the other end of the blue wire to the remote input on the amp, connect power and ground on the amp.
plug in all required connectors
Connect power, ground, accessory on the radio
you should be ready to tune the system now.