I started over with a clean install of 10.12.3. I followed exactly the directions from conath 12/15/2016, The "Unintentional Hack Pro"
https://www.tonymacx86.com/threads/...-gaming-skylake-i5-6500-macos-10-12-3.209909/
His instructions are like many others.
My MoBo is different (GIGABYTE Z170X-UD5 TH) and the brand of the RX 480, mine is Sapphire.
I used iMac 14,2 in MultiBeast.
It all worked.
I have acceleration and
metal is supported. I had never been able to patch the AMDRadeonX4100.kext and have it reboot. This time it did work. I have to change the HDMI cable after clover at bootup. I did the other things mentioned in his post including the KextsToPatch in the config.plist file. That did not change the incorrect name (as expected) in the System Information and it is still AMD R9 xxx 8192 MB.
Resolve Studio and FCPX 10.3.2 both work.
Next, add the second RX 480 for Resolve rendering.
Maybe Thunderbolt, which does work in Windows 10 Pro on a separate drive.