I built a system using this board last week and I'm writing this comment on it right now. It's still early, but I like it so far. I got it because it was one of 2 mini-ITX boards that had both USB 3.1(A&C), and an M.2 slot. And it had about double the USB 3.0 ports that the competing Gigabyte board had.
I notice you were using the P1.2 BIOS. When I built this, the current BIOS was 1.5 and one of the major parts of the updates was memory compatibility. I wonder if you'd have any better luck with your memory issues with a newer BIOS. I'm using Ripajaws V @ 2800MHz with a locked i7 6700. It took some fiddling to get it to boot with both sticks in, but eventually it worked with the default XMP profile.