I need to pack away the 2.5" drives, but I do have 10 drives running in the MS Gen10. I have Windows 10 Pro running on a M.2 Crucial SATA SSD and a Toshiba M.2 NVMe PCIe mounted on the top PCIe card in the picture below:
The bottom card is a Marvell based 4 port SATA PCIe x1 card, that is running four 2.5" drives. When buying cards for a MS Gen10 be sure they are not taller than the bracket.
Here are the cards I used: