Dual Monitors not Working in High Sierra

I have:
Intel Core i7 7700K 4.2 Ghz
Gigabyte GA-Z270MX/Gaming 5
Samsung CF791 Series 34-Inch Curved Widescreen Monitor (C34F791) 3440x1440 4K
Samsung U28E590D 28-Inch UHD LED-Lit Monitor with Freesync support 3840x2160 4K
XFX AMD Radeon™ RX 580 8GB 256 Bit GDDR5 Graphics Card

Both monitors are hooked up through Display Port
Sierra works fine and I get full 4K off both monitors and everything works. However....
With High Sierra
I can only boot into High Sierra with 1 of the monitors turned on. Whenever I turn on the 2 monitor everything freezes within High Sierra and screen goes gray. I can still see the desktop but can't click on anything.

Anybody know what I can do to get both monitors working fully in 4K?

Some Success
-------------
After 2 days of constant testing with no luck. I think the problem has something to do with the AMD .kexts in S/L/E. When I copied the AMD .kexts from Sierra to High Sierra I got weird colors (red & blues flipped) and the 2nd monitor will go on and not lock up the computer

Even though the method of copying kexts somewhat worked... It made the graphics choppy and everything was running slow (open windows and programs).

Is there a FakeID (FB Name, NVCAP, VRAM, Video Ports, Display-cfg, ig-platform-id, BootDisplay) of some sort I can use in Clover to fix this? Kext?


My clover config is attached if that helps anybody!

Also...
The 2 pictures attached are what happens. Boots with 1 monitor on. As soon as the 2nd monitor is turned on or plugged in... The working monitor goes black and everything stops responding.

Hello Gogeta5026

I have the same problem with my R9 270X card, On Sierra it works without any problem.
With High Sierra i get one greenish glow screen and one normal screen, it also mirrors the screens.

Hope someone knows how to fix this, or it will be fixed in de release next week.

What cool curved monitor is that? is that a TV or monitor?

I am currently trying to get dual monitors working in Sierra. Cant boot with both monitors connected. One DVI, one HDMI..Frustrating

Thanks, my monitor is:
Samsung CF791 Series 34-Inch Curved Widescreen Monitor (C34F791)

Gogeta5026 said:

Thanks, my monitor is:
Samsung CF791 Series 34-Inch Curved Widescreen Monitor (C34F791)

Click to expand...

Have you tried the Framebuffers Baladi, Berbice, Orinoco? You can enter them in clover boot manager screen.

Same issue here with Sierra. I built the setup to work with PC and Mac at the same time but I can't hot plug the hdmi so if I swap my monitor to PC I can't go back to MacOS without a crash.
I think I will start from beginning because it is supposed to work I guess.

Gigamaxx said:

Have you tried the Framebuffers Baladi, Berbice, Orinoco? You can enter them in clover boot manager screen.

Click to expand...

I know I tried "Baladi". I'll try the other 2 when I get home from work in about 5-6 hours. THANK YOU!!!

WE GOT SOME SUCCESS!!!
Orinoco plus Inject ATI plus Dual Link=1. I'm fully booted with no crash, both monitors work.

1 PROBLEM.... 2nd non-working monitor, from before, is just a mirror of the 1st. 2nd monitor is not showing up in Display Settings.

Worse comes to worse... I have a Radeon Vega Frontier Edition coming in the mail tomorrow. Saw somebody, ON THE OTHER SITE, build a working one with an identical motherboard, CPU, etc.

Attached is my config of what got me this far. Maybe there's just 1 little tick or # change I need to get 2 monitors recognized in Mac High Sierra.

Hello Gogeta5026 Did you find a fix for the problem ?
With the release of HS I hoped it would have been fixed but I still can't get my dual monitors to work.

Can I ask how did you connect your screens, by VGA ?