I have been using OMV
I have got the Allnet 4port sata m.2 pcie card which works great but afterwards wondered if I should of took a chance on a 5port as that extra could give you a ssd write cache option or a RAID6 posssibility.
I don’t think it has been tested by anyone but its very likely to work…
http://www.iocrest.com/en/product_details623.html
Same though just using the above pcie power string to female 5.5/2.1mm barrel for sata or just a splitter to USB.
I wouldn’t use USB for RAID and also would not use Sata RAID for large file media stores, but both work excellent for specific uses.
The 3.0 usb cards are really cheap but it is only a single pcie2.0 lane but they work but bandwidth is shared.
I am wondering if to give one of these a go but a bit pricey & with 2x usb3.0 already there is existing bandwdth.
https://serial.en.taiwantrade.com/product/shentek-2-port-internal-usb-3-1-m-2-card-1821126.html