Great guide, trying to do this in my 2010 outback, but after sodering i do not get any sound, and i belive my harness is somewhat different.
I do have the 20 pin connector to amp, but i only have one light blue cable in the DIN 20 pin and only one Amp, it have subwoofer in the rear.
I have also testet this pinout guide, but still no sound. https://pinoutguide.com/Car-Stereo-Subaru-Suzuki/Subaru_Mclntosh_PF-40621_pinout.shtml
Never mind, it was the remote amp from HU that was dead put it on ignition and voila
Br from Norway