Haha after 3 days struggling I finally achieve the impossible, 6x1080ti on a AM4 motherboard mining guarantee, not counting 2x M.2 slots. I could achieve 8xGPU if i have enough part which are on the way shipping.

Spec: Ryzen 7 1700, Asrock X370 Killer SLI/ac (2xPCIe 16X + 4xPCIe 1X + 2 SATA/PCIe NGFF M.2). Windows 10
Riser: 6x Ubit riser latest version with LED. One came defective, contacting them for the replacement.

So with only 5x riser on hand the only possible way I think of is one of the GPU must be connected directly to the pcie 16x on the motherboard and it's just how i did it. So here is how:

1. Download this portable freeware and have it ready http://www.guru3d.com/files-details/display-driver-uninstaller-download.html
2. Download latest driver for your GPUs and have them ready.
3. Download and flash latest BIOS for your mobo (mine is version 4.50 2018/1/16)
4. Go to your UEFI/BIOS, find and enable "IOMMU" equivalent to "4G decoding", also change 2 PCIE (or PEG) options to "GEN1" (forgot what exact settings are but its there).
5. Always reboot or startup your system in SAFE MODE during GPUs installation. (WindowsKey > msconfig > Boot tab > Boot option: safe boot). Repeated this everytime you reboot your computer for a great chance to success.
6. Boot in safe mode, run DisplayDriverUninstaller.exe, choose Clean and Shutdown.
7. Install your GPUs, all at once or one by one (like i did) whichever work for you. My setup is 5 GPUs via risers and one in the slot 2 PCIE 16X.
8. Patiently* boot in safe mode. Check device manager to see if 6 GPUs show up. If they do appear then go ahead and install driver, reboot to normal mode and enjoy. If not then repeat carefully. As long as I reboot into safe mode all my steps are solid and work 100%.

*After new GPU(s) installed, the main display should be the GPU installed on the first PCIE slot aka PCIE slot 1. Either that or try to plug your display cable (HDMI/DP/VGA...) into the PCIE slot 2. Worst case then try all other GPUs until windows show up on your monitor.

Also I don't recommend any MSI boards for this example unless they are made for mining. Look at their mobo specification they tried to hide as much information as possible, the missing information can only be found in their specify manual of each mainboard. What they hide are some SATA and PCIE lanes will be disabled if there are devices connected to the other lanes. That pretty much explain why MSI's owner has no luck stacking their GPUs. Best brand for experiment should be Asus and now I just found out Asrock too: No PCIE lanes are disabled no matter how many you plug in, they have a better chance to work. Also Asus and Asrock board mostly come with 6 or more PCIE and 2 M.2 which is a plus for both of the brand.

Well, I think I cover almost everything I did to get 6(+2) GPUs working on a AM4 motherboard. If you think i miss anything or have any question please send me a reply. If you find my post helpful please share them as much as you can. I am an AMD fanboy and I want AMD to be popular not only in gaming but also in mining. I'm looking forward to build my 2nd rig with Zen2 if possible. Good luck and happy mining.

Edit: Here is proof guys.https://imgur.com/a/xoTqY

macabong

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