Saberus :
Given that they mount into the PCIe slots and thus are directly under CPU control, I would say your only option is software-based RAID, with the OS running the controller functionality.
Why are you wanting to do this?
Also note that some enterprise and performance grade PCIe SSD cards already run a RAID 5-like mode internally (Using each chip or group of chips as a 'physical disk') and present the full volume as a logical drive.
Blueberries :
With a new motherboard you can RAID two AHCI x4 M.2 drives, if you feel so obligated.
So you guys are both recommending software based raid, but if I were to use motherboard raid, wouldnt I be limited to the speed of the PCIE bus on the board? (which would likely be slower than the max speed of raided pcie ssds no?)
Side note: I did not know that Saberus, thanks