Cannot Recognize 5th Sapphire Nitro+ RX 470 on PCIe 1x16 Riser

[Drawde]

MSI Z170A GAMING PRO CARBON 7GPU
4 Nitro+ RX 470, 3 on 1x16 risers, 1 on MB
Windows 10 Home, UEFI install mode, 120 GB SSD
BIOS, Settings -> Advanced -> PCI Subsystem Settings
Change ‘PEG0’ and ‘PEG1’ values to ‘Gen1’
Set ‘Above 4G Decoding’ to ‘Enabled’

All works fine including mining but when I add the 5th GPU on a 1x16 riser it doesn't start, no fans startup as is normal for any recognized GPU. I tried other risers and another PCIe slot with the same results. I even replaced the GPU because I thought it might be defective but I continue to get the same results.

Any other ideas what could be going wrong here?

[adaseb]

The Z170 chipset doesn't support 5 or more GPUs.

[Drawde]

The Z170 chipset doesn't support 5 or more GPUs.

I think there are people using it with 7 GPUs. I neglected to mention I also installed the custom BIOS mentioned below.

https://bitcointalk.org/index.php?topic=1819611.msg18124988#msg18124988

http://1stminingrig.com/msi-z170a-gaming-pro-carbon-motherboard-review-mining-performance/