I tried changing IOU2 to 4x4x4x4 in bios, as I think that maps to slots 5&6 based on the motherboard diagram (low confidence here), no change.
nvmectl devlist (am running freebsd) only shows the kingston in the motherboard socket, neither of the drives in the riser.
I have nothing in any other slots, as mentioned in the other comment – just the m2 on the MB and dual riser, with 2 drives in it.
I’d like to put it in slot 3, and I do get one of the drives to show up if I have it there.