To be able to maintain climate control, we will need to split power and send it to the headunit still. Thus you will need a Reverse and Forward facing Subaru radio harnesses, plus antenna adapter.
Issue with most aftermarket forward facing harnesses is they are missing Pin #7 which is for illumination an is important! I simply bought two of them and stole a pin from one of them.
You can test the fitment/resistance of the wires with your two plugs
Depin the reverse facing harness, remove speaker wires, antenna etc, leave only power/ground and illumination wires. You don't want to have those wires to be even in there, otherwise you can get a short and kill your factory radio.
Crimp/solder heat-shrink and your done
Back to hooking up the radio, the factory radio has three additional plugs that need to be hooked up along with your reverse facing harness.
Plug up the aftermarket head unit, you can see the antenna adapter here too
After all is in place, checking airbag module clearance
Done for now, nice to have USB playback again!
And you can make out the radio from drivers view, which is a nice plus.
This ran me up about $30 with all of the harnesses/adapters. I now have good music for some long trips coming up, I may switch to a proper JDM unit in the spring, but I would rather spend the money elsewhere if this lasts.