Am I understanding this correctly, as in rx480 cards will work OOB with 10.12.3?
Very interested in this because I'm building a Hackintosh on a x99 motherboard and I wanted to use this card.
You will need a helper graphics card and one 16 lane pci slot and one 4 lane pci slot. If you can configure this in bios you can make it work. They're not OOb completely, you need to make a few adjustments but most are able to get them working and use them for graphics work. They along with the newer AMD cards need bios settings for igpu or IGFX as primary display, or integrated graphics mode. If you don't have graphics on you CPU you can use a lesser " native supported (OOB)" card as integrated graphics and it works. One user in the testing thread with an X99 system has a 1070 in slot one 16 lanes, and an RX 480 in the #3 slot with 4 lanes for the RX card. In Windows he has the 1070 and then when he boots into Sierra the 1070 lists as display 5mb, but the RX gets support and functions well.
I've tested this using my Z170 in dedicated graphics mode and it works, it's not as good as with igpu (CPU) and RX card it loses about 10% performance. However, z170 systems only have 16 lanes total so an X99 with more lanes available (CPU) dependent should work a lot better.
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