i saw an article regarding z170 raid.
but do you think is only hardware problem?
intel RST as see in specification detail support nvme Download Intel® Rapid Storage Technology (Intel® RST) RAID Driver
Installs the Intel® Rapid Storage Technology (Intel® RST) RAID driver version 220.127.116.119.
This driver supports RAID 0, 1, 5 and 10. The driver should be installed after the operating system has been installed. F6 and RAID BIOS configurations need to be performed prior to installation of this driver for proper operation.
This driver supports NVMe devices. ""
As you have mentioned, There is no RAID support for NVMe drives with IRST on the X99 chipsets, so you will not be able to use your new drives in a RAID configuration. That chipset does not have the PCIe/SATA remapping technology required for RST to support NVMe devices. IRST only supports SATA devices on the X99 chipset.
You can find more information in a related thread: Re: Configuration Question