I just tried to use a pair of the Sandisk X600 M.2 in the ASUS P10S WS motherboard.
Bottom line, don’t try it.
The pair of X600’s were configured as RAID 1 (i.e. Mirrored) and when I booted off a USB drive to install Windows Server 2012 R2 it would usually hang (9 times out of 10) at the spinning dots after the initial loading of files off the USB drive. You would seldom get to the questions asked by Windows setup. The motherboard Q-Code displayed A0 (IDE Initialization is started) during the hanging spinning dots.
The motherboard is on the latest BIOS 3105 and I was able to confirm, off an older installation of Windows 2012 R2, that the X600’s were on the latest firmware as of this date using the Sandisk utility.
Normal diagnostic procedures such as removing all other cards and drives and resetting CMOS were attempted. I have used another vendors M.2 SSD’s in this motherboard successfully with Windows Server 2012 R2.
I have fallen back to a pair of SATA SSD’s and performed a clean install.