It must be the power requirements within the motherboard bios, rx 480 was an 8 pin maximum, some rx 580 has 1 8 pin and 1 6 pin so in turn. mb bios is not accepting that cause mb power running amperage is way higher. The issue relies on motherboard bios, need to mod the motherboard bios for it to accept 6 cards or more. If you think about, it makes no sense why is not working. It should work. I advise you to try 7x rx 570.