I have a R9 390 from sapphire and had a lot of issues with it since High Sierra. But I got it running. I did the following. - selected igpu in bios as primary - connected the igpu to the monitor via VGA cable - connected the r9 390 to the same monitor via HDMI - booted with the following options in graphics section: Injectati=yes Id: 0x67b01002 FB: Radeon Port: 04 Load Vbios= yes And then for the igpu I also selected inject and changed the id: Id: 0x12345678 Boot it up, switch to second input on the monitor, log in and it will show you 2 monitors in settings menu...I then selected the hdmi input as "main" screen. Good luck.