Well, i dont' think you can do that.
The way it's wired up now is that your HU has the pre-outs and it has it's own amp(45x4 or something like that) Well, the speakers are hooked up to the HU's amp. Now your going to be using an external amp. So the HU's preouts go to the amp, then speaker wire from the amps channels to your speakers. You will have to remove the door panels for the door speakers. I haven't wired my speakers to my amp yet BUT i have replaced my stockers in the front. The door panels aren't difficult to remove, you could hook up your speakers in probably 1 - 2 hours, depending on how much trouble the screws gives you.
Click to see how to remove door panels Make sense?
You could probably run the speaker wire and splice into the wiring from the HU but....I'm not sure if it's a good idea. It could be. I'm not going to do that though. Not worth it to me, plus, I've already got a splicing mess back there
