Thanks for the amazing SVXdc (David) this project is now officially possible without ripping off your whole car harness. I'll be retrofitting this into a 2013 WRX Hatchback.
Here are the parts that SVXdc (ae64.com) have for you:
A) 10-pin and 6-pin reverse power/speaker harnesses (Toyota style), with all pins that the FM601US needs.
B) 20-pin "forward" harness, with 3 SWC wires connected to 28-pin reverse harness.
C) 28-pin reverse harness, with aux and mic pins connected to a 16-pin "forward" socket. 28-pin harness also has plain wires for reverse gear and vehicle speed signal (VSS).
D) Hirose female 4-pin USB socket
E) 16-pin reverse harness, with any or all of these that you want: wires for parking brake, rear camera RCA jack, and 6 Volt camera power supply.
You will need to:
1) Solder or crimp A to B (14 wires).
2) Connect VSS wire from C to your car's factory VSS wire.
3) Connect reverse gear wire from C to your car's factory reverse gear wire (this may only be needed for camera function).
4) Connect parking brake lead from E to chassis ground.
5) Swap your WRX's mic module with the mic module taken from the map light cluster from a car with same FT nav.
6) Build a USB adapter (from my Hirose socket to a Toyota-style USB plug).
7) Buy a reverse Lexus antenna adapter (Metra 40-LX21), connect from FM601US to the Motorola plug on your WRX's factory antenna adapter.
8) Obtain a Toyota-style GPS antenna (Subaru or Scion/Toyota have this for about $175)
So SVXdc found out that certain type of Eclipse GPS antenna might work as well. I ordered one from ebay and will post more info on whether it will work or not.
For the USB: SVXdc and I are still researching this. The socket on the back of the Fujitsu Ten unit is a socket typically used by Toyota. SVXdc mentioned that Subaru or Toyota might have a short breakout harness/cable with the toyota style plug I can buy to crimp/solder to his hirose socket. He also mentioned a electronic parts website that might carry those plug. I'm still waiting on his reply about this. I'm sure he'll be able to find a plug to make this work as he found the impossible 28-pin connector.
Your OEM bluetooth mic won't work properly with this head-unit. Reason is because the mic from non-nav cars has an amplified circuit that causes gain problem with the Fujitsu Ten unit. You need to buy one from a car with the same HU or buy the complete dome assembly from Subaru/crashed car with the FT nav.
The OME bluetooth mic worked fine.
Update: I just finished installing the FT HU into my car. It started up just fine.
I am still missing the GPS antenna, and the Toyota/Lexus radio adapter. But bluetooth actually worked flawlessly. The oem mic even works perfectly.I'll have to check my connection on this when I take the HU out for the antenna.
There is a problem with my aux input however. It doesn't have any output on the right speakers (actually very low output even at max volume).
It was the aux cable I used. Replaced with a different aux cable and it worked fine.
Still no USB function yet. I'm still hoping SVXDc can find an adapter to make this possible. Otherwise I'll have to open the HU and solder wires onto the PCB to the Hirose connector.
There is a BIG improvement in term of sound quality. Much better bass and louder volume without distortion. And all this is just through Bluetooth streaming. I can't wait to see how USB/Aux, HD radio, and CD perform.
Please don't PM me asking how-to. Post all your question here.
Update: SVXDc has found the part# for the USB harness you can get from Toyota or Subaru to splice into the Hirose USB Socket.
86273SG230 2014 Forester USB interconnect cable
List: $120.73 Online: $88.38
PT546-00120-US Toyota USB harness
List: $74.04 Online: ~$55