I checked it out and the SM951 is a PCIe, but the M.2 port on the board only accepts SATA and PCIe is not supported.
But to answer your question, I had tried it with both RAID selections, enhanced and AHCI and none of them worked. I've installed the OS in UEFI configuration.
Do you have any idea about the big delay before BIOS load?
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The 30 seconds delay will happen every time you power cycle the system. That time is what the BMC (Baseboard Management Controller) takes to initialize. During a reboot you should not experience anny kind of delay.