You arent really running them in AHCI. The BIOS setting is misleading. It should really say raid enabled/disabled. NVMe and ACHI are two different protocols.
You cant build a raid array from the BIOS. My guess is your second drive is not properly initialized. Get the latest IRST drivers and IRST software. You build the array from within the OS.
Im actually a bit surprised they changed the Toshiba Drives as they are not all that common place. OCZ is limited supply and honestly Ive always dodged OCZ products like the plague. There isnt much info on the OEM drive so they may not even be compatible to be used in a raid 0 array.
I can vouch for the Samsung 950 pros in raid 0 but not OCZ with OEM Toshiba.
http://www.win-raid.com/t2f23-Intel-RST-RSTe-Drivers-newest-v-v-WHQL.html
“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein