Ok, unplugging the mouse and keyboard didn't do jack. 

I'm getting more and more convinced there's a major issue with this board.
I tried booting up smOS via the onboard VGA after reconnecting my 4 GPUs and I was greeted by the "please install the PSU's 4-pin power cables to the 4-pin connections on your motherboard" screen DESPITE using powered risers AND having those 2 molex connected to the PSU... 
I ignored and booted anyway and the whole thing restarted after 10 minutes or so after a fan gradually started doing a funny noise. 

Also smOS couldn't seem to connect to the internet. 

I'm bummed. Big time.