I have seen miners slip with 7 GPUs on that motherboard on this board, but haven't seen it done with 8. I have just googled it, and it seems a lot are doing it like these:
http://cryptomining-blog.com/8700-8x-gpu-nvidia-mining-rig-with-asus-prime-z270-a/
https://steemit.com/crypto/@cryptos/8x-rx-580-gpu-crypto-mining-rig-with-asus-prime-z270-a-motherboard