High Sierra 10.13.6 will recognize the Sapphire RX 580 Pulse 8GB graphics card OOB which is why I'm using this card is serveral of my rigs. You may have problems with other brands/models of AMD cards.
To switch graphics cards, first boot using the GTX 960. In the config.plist, set the SystemParameters/NvidiaWeb = No. Then, remove the Nvidia drivers using the Nvidia System Preference pane Uninstall option. When it wants to reboot, shut down and install the Sapphire RX 580 Pulse 8GB graphics card. That should do it.
Just bought a second hand Sapphire Pulse RX580 8 gb today, and followed your indications. It *almost* worked OOB : I get a purple screen when logging in to OSX ( I'm still on High Sierra).
I am using a DVI-to-HDMI cable to connect to my monitor, this scheme has been working like a charm with my previous GTX 960 board for several months. So I replicated the same type of connection when I first plugged in the RX580 but bumped into that purple color problem.
Note that on booting, either into UEFI or during initial "Apple loading" , the colours are perfectly normal - the while apple is really white. It's only after the hackintosh gets into login screen that the screen becomes purple.
I got rid of that issue by using a HDMI to HDMI cable plugged into the HDMI port of the RX580 instead of the DVI port.
So , the question is : what could have cause this purple screen when I use the DVI port ? When I connect the DVI-HDMI cable to a secondary monitor ( my tv screen in fact) the tv screen inherits from that purple tinge, while my main monitor ( i.e using hdmi-hdmi connection) displays correct colours. Any idea what could be wrong? I checked in the forum, and there are a couple of cases mentioning a quite similar issue, but I could not really make sense out of the threads . More specially I do not understand why this connection worked fine with my previous nvidia GTX 960 and not working correctly with the RX580.
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