Hi Eric,
If you stripe 3 of your internal drives under RAID 5, say if you have 1TB each. Instead of getting 3 TB, you will end up something close to 2 TB for you to use .
Using 3 regular sata drives under RAID 5 will let you edit 4 streams of ProRes HQ according to apple’s site. I think if you want to do 10 bit uncompressed HD, you will need to use 4 drives which like you said it’s not recommended.
Caldigit has a similar products call caldigit raid card which they claims to have external ports to connect more drives(more speed?). Maybe you can call them up or check out their website. https://www.caldigit.com
Good luck