@Thehack is right, I went back and forth with him about a year ago on using the DA-2 in this way. You will need to find a board that accepts 12v input directly. Take a look at server/workstation boards like those from AsRockRack or SuperMicro and you may find ones that would support this. @fabio did a similar build with a Meanwell 12V PSU and the ASrock Rack C246 WSI motherboard.You can only do a direct ac-dc to motherboard if your motherboard supports 12V in.
100% of it needs to go into the Picopsu.