Im using several Asus Z270f boards with 7 cards each, without a hiccup. Just turn on above 4G decoding, put all pcie to gen1 and disable everything you arent using.
I have the same board and 1060 cards, but for the life of me I cannot get past 4 cards. 4G is enabled, also tried PCI speeds of Gen 2, nothing. 4 is the max. Any suggestions or pointers?