disable fastboot and csm. try 100bclk too instead of 125bclk (i guess your tridentz are 3200mhz) this forces the m.2 to run at gen3. it will drop to gen2 if youre using 125bclk (just disable your xmp profile, this should let it run at 2133mhz/100bclk)
I tried this:
M.2 drive connected
2 HDD connected
PS/2 wired keyboard/mouse
CMOS reset button on rear (green - black - green)
Unplug power at wall 10s
Plug power at wall
2 HDD detected on SATA controller 1 and listed
F1 to enter Bios
Check RAM @2133 (from CMOS reset) and BCLK is 100.
PCH Storage SATA controller 1 set to RAID.
Hard Drive BBS priorities Boot option 1: N1-Samsung 950
Save and exit
Cannot access CTRL-I for RAID setup
I can activate BIOS or let it go through to M.2 boot
If I enter Bios, M.2 drive no longer listed for Boot option #1
You must have CSM Disabled for Samsung 950 pro to work properly. If you have CSM Disabled you cannot access raid setup with CTRL-I any more... You have to setup your RAID disks from inside UEFI BIOS. Look in Advanced menu the last option... There you can setup your RAID Disks and everything will work as is should!