Success. Got iOS loaded. But then things get funky in post installation. Had to go into Bios and change Gpu to onboard intel instead of PCIE.
First, there are all sorts of digital artifacts in the tabs of the browser. Crazy graphics stuff. I tried loading your 580 driver but had a bit of a dance with the system. plugged the HDMi into the 580 and things went whacky. n reboot, got a black screen. Then went back and forth between onboard and external GPU. Got the circle slash symbol, booted in safe mode and made some changes of which I have no recall. But I'm back in the software again.
I'm going to look over what you've accomplished here and do a step by step stabilization.
You said that after install, the HDMI could be fixed. Working on that.
And then dive into Bluetooth/Wifi. But more for the hand off and all other Apple extras. Also need to get the wifi module
Then TB3
Thanks for your help thus far.