To make ASUS PRIME H270-PLUS motherboard work with 8 video cards the following BIOS options should be set:
- Advanced\System Agent (SA) Configuration
- Above 4G decoding [Disabled] -> [Enabled]
- DMI/OPT Configuration\DMI Max Link Speed [Auto] -> [Gen1]
- PEG Port Configuration\PCIEX16_1 Link Speed [Auto] -> [Gen1]
- Advanced\PCH Configuration
- PCI Express Configuration\PCIe Speed [Auto] -> [Gen1]
- Advanced\APM Configuration
- Restore AC Power Loss [Power Off]->[Last State]
- Advanced\Onboard Devices Configuration
- HD Audio Controller [Enabled]->[Disabled]
- M.2_1 Configuration [Auto]->[PCIE]
- M.2_2 Configuration [Auto]->[PCIE]
probably not all of these settings are strictly necessary, but at least I was able to connect 8 video cards GeoForce GTX 1060 with them: