I've reached out to several third-party software suppliers and the only one that has responded thus far is NIUBI Partition Editor. Not sure if the Windows command prompt procedure can be use while the drives are configured in IRST, but I suspect the RAID would first have to be removed? I have been through all the options in the BIOS and haven't seen anything there that could be used to alter a partition. This is not a problem since there are excellent instructions here for installing and using the product. And it has absolutely no guidance, they defer to Intel.
In fact, the only RST version they are recommending / including in their official drivers and software downloads is Intel RST Version 17.
Thank you Deivid for your quick response and suggestions!