Installed the Pioneer GMD1004 Amp over the weekend. Made a big difference to the previous Focal speaker upgrade i did earlier - it can drive them a bit harder. The amp introduced a slight hiss to the speakers, but I think that is normal for a speaker-level input amp. It's not really noticeable when driving, only when stopped, and the improvement in sound makes it well worth it.
I used a different wiring harness: the Aerpro CT10TY01 ISO T-Harness. This one harness is all you need, can be bought on ebay for about $30. Says it's for a bluetooth kit, but worked fine with this amp. The power cables are decent thickness, and since this is a low powered amp, and the stereo already has a 20amp fuse, I didnt run a separate power line. Works perfectly.
FYI here's a good video on how to get the dash apart to get behind the existing stereo:
https://www.youtube.com/watch?v=6PcPsEG1SpcAmp and wiring harness, showing how the cables plug together.
Red arrows show the 2 plugs that connect to the wiring harness.
Wiring harness connected to existing plugs
The amp itself I installed under the centre console, plenty of room down there, and the cables are plenty long enough. I stuck it to the base with a few sticky velcro pads, and cable tied up the cables to keep it from vibrating or moving around.
So overall I'm really happy with the result. Looks and functions as stock, but a huge improvement in sound. Pretty easy installation too - the Focals took about an hour to install, and this amp took another hour to install.
One strange thing I noted, after putting everything back together, and putting the Battery Neg terminal back on, that the pic on the dash that shows which door is open was backwards for the front doors! Ie with the drivers side door (R) open, it showed that the Left front door was open, and vice versa. Confused me a bit as I didnt think I had unplugged anything to do with the door switches. I pulled everything apart to double check that I hadnt missed anything, and it still was the same. So I though it must be a programming issue after disconnecting the battery, and was going to ask my dealer to fix (due for a service soon). But then when I started the engine, I noticed the door indicator on the dash instantly flipped back to normal! So starting the motor must have triggered the programming to correct itself again.
Just thought it was worth mentioning in case anyone else saw the same thing - it should correct itself.