Just wanted to contribute some updated information for us with the 13/14 Nav+HK systems to installing new headunits with Apple Carplay/Android Auto.
Here's the original link you will need for pictures, new center trim, and dashkit: 2013/14 HK stereo w/ Nav headunit upgrade
Thanks to the OP!
What you will need from Idatalink:
1. Maestro RR2: https://www.idatalinkmaestro.com/en/products/maestro-rr2
2. T-Harness for Subaru's (this is what they call the harness that connects the RR2 to the factory plugs): https://www.idatalinkmaestro.com/en/accessory/1377/HRN-HRR-SU2
(Make sure it's the HRN-HRR-SU2, NOT the HRN-RR-SU2...unless you don't like plug-n-play and want to figure out wiring diagrams.
What you will want from Idatalink:
1. The specific wiring harness adapter from T-Harness to your radio (i used a pioneer unit https://www.idatalinkmaestro.com/en/accessory/1275/ACC-HU-PIO1)....unless
you don't like plug-n-play and want to figure out wiring diagrams.
Don't get the USB adapter, it won't work.
The install .pdf is attached. There's one thing incorrect in the .pdf that I learned after calling tech support (which is quite great, btw) you will need to use the B harness adapter provided (and shown at the bottom of the .pdf) to connect the blue and yellow plugs on the harness. The factory backup camera will not work otherwise.
If you purchase all of those things, it is 100% plug-n-play and is actually one of the easiest headunit installs I've ever done.
Also another thing of note, that isn't mentioned anywhere, the factory microphone isn't reused so you will need to install the microphone that comes with your headunit.