Sorry for the late reply. How did you install Win? I've done mine using a win 10 stick and not using bootcamp. Not sure if this makes any difference.
I got it working by - restart your laptop, when the chime comes on, press option to select the startup drive, and right after, plug in the box. Wait for a few seconds, then select the windows partition. It gets recognised about 1 in 10 times. If you reboot more than twice and get the infinite loop, it will go into auto repair. Unplug the box, restart, wait for the auto repair to do its thing, then try again.
Either this way, or plugging it in right at the first 'wheel spin'.
Got it working superbly stable, but with an external PSU and the barrel plug mod.
Now I'm trying to get my head around a 2016 13'', the same box, but with a EVGA card..