Theres the plug mate.
Thanks Antony
They are high level inputs from the left hand rear and right hand rear speakers.
I was trying to match up the colours from your picture to my diagram. It's a bit hard to see some of them in your picture, but I am pretty sure this is what you need.
If you can match my colours with the ones on your plug, you are in business. But you will need an amp with high level (speaker) inputs.
The wires you need are -
Yellow/light blue trace and brown/black trace are from the left hand factory speaker.
Light blue/orange trace and light blue/black trace are from the right hand factory speaker.
I don't know which is positive and which is negative, as it doesn't say in the diagram I have. You can work this out with a multimeter.
The two orange/light blue trace are +12 volts
The other wires are for the factory sub speakers and earths to the factory amp.