The door wiring looms go into the cabin via a plug/socket assembly on the cabin side. Undo the single bolt with a wrench (size 10). You can do this without having to take the door off. Once the bolt is loose, unplug the wiring loom. Take off the door trim and push the wiring loom into the door and pull it out from the side. The socket on the cabin's side can be unclipped and pushed in. You can pull it out after you take off the kick panel.
The plug and socket have quite a few empty spaces where you can put in additional pins to run additional wires. Alternatively, if you only want to replace the original speaker wires, no additional pins are needed. Just find out which wires are for the speaker and take the corresonding pins out and connect thicker wires. No drilling is required.
I had to do this when I installed a door lock actuator in the driver's door in order to use the keyless entry function of my alarm.
Good luck.
