So, trying to sort a better headunit in the A3 than the ****ty JVC one that was in it when I got it.
Managed to get my Sony one working eventually after much arsing about with the wiring loom from halfords.
However, only one front speaker works.

I had sent the below pic to the lads in caraudiodirect and they sent me THIS adapter, as you can see though, it has one more plug than I have.

Also, I checked in the boot and there's no amp or sub.
The fella before me had fitted 6x9's to the parcel shelf and butchered the old radio's harness to wire them in. Would it be possible that he disconnected the original wiring to the stock rear speakers or are they not working because the sub and amp are missing?

Also, from my pic, is that a non Bose or Bose set up?

 

It appears that you have a non-BOSE setup. The brown plug is for speaker connections. Did you see another black connector in there somewhere? it would have 20 pins in it. The red plug, from your vendor, is where the CAN BUS info goes.