Asrock B250m pro 4 works like a charm with m2 adaptor. I have one that is not the usual 4x pcie slot but a usb connector. Been using it for days together with two cards in the 16x slots. this mobo does 3 cards like that. Gigabyte z270p-d3 also works fine with M2 adaptor, running 5 cards now.
Do you mind letting me know what settings in the bios you had to use to get 5 cards running?
I have the same board. going to be running ubuntu, with the riser setup - 2 m.2 to pcie adapters, and then 5 risers (3 to the regular pcie and 2 to the m.2 adapters)
ill be using 1060's
is it just set 4g decoding to ON and then the upper memory lower (tulad? w.e that is) to 1gb?