What motherboard should I buy?

I need a 6 gpu motherboard. I can't do to work my MSI x370 Gaming plus with 6 gpu. Dosn't have an option for down pcie gen and when I put "above 4G decoding" on, Windows 10 won't start. Just detect 4 gpu.

This is my options on my country:

Asrock Fatal1ty Z270 Gaming K4
Gigabyte GA-Z270 GAMING 3
Gigabyte GA-Z270 Gaming K3
Gigabyte GA-Z270X-Ultra
MSI Z270 Gaming M3
MSI Z270 GAMING PRO CARBON
MSI Z270 KRAIT GAMING

Is for 6 gpu + Pentium G4560 + 4GB DDR4 RAM

Thanks!