MSI Z170A GAMING M5 is in the fully supported list, this mobo has 7x pcie and 2x M.2 slots, so it might support 9 cards. I tried and found that only the 1st M.2 slot(near CPU) worked with M.2 to pcie adapter, so I can run only 8 cards. Any body tried 9 cards?
I use Asus Prime Z270-a. In its bios you can change the function of the m.2 slots. Now I use it with 7 card because the m.2 pcie adapters have not arrived yet, so when they will arrive maybe next week, I will referee to you is you need it.