You MUST have above 4g enabled to get more than 4 cards working.
First, make sure that Windows is installed in UEFI mode. If not, you will have to reinstall.
If Windows is installed in UEFI mode, then try this:
Plug only 1 card in, disable above 4g encoding, use DDU to uninstall drivers, reinstall drivers, use pixel patcher, restart and set bios to above 4G enabled. If Windows boots, then plug 1 card in at a time until you get 6.
For drivers, if you have RX 480 then use 16.x.x driver. I personally use 16.9.2.
If you have RX 580, then you have to use 17.x.x driver, but use mutated version that has 16.x.x files. Search the forum, this has been posted multiple times.
Thank you, I've tried variations of this from what I've read hear and couldn't get it to work. This order did though, appreciate it!