So000...FWIW - I believe you need a special "enabler" card thats support SFF-9402 standard - I believe the part number is: 05-50061-00
1m 2 SFF-8643 to 2 SFF-8643 NVMe Cable - 05-50061-00
Ordered a pair to test/confirm.
I got my cables in - They work! BUT there was a caveat ... If you use the first 2 ports for NVME, the last 2 ports will only do SAS2 / 600MB or SATA3 / 600MB/s. So for an SATA 3 or SAS2 array these will work exactly like you want.. But for my SAS3 Array - I loose the 1200MB/s and go to 600MB/s for the 20x SAS3 drives. For most this is more than enough, but my SAS3 do 800MB/s+ so I'll take the extra bandwidth, vs gaining a PCIE slot back..
Suffice to say I have 2x pairs of these special cables up for offer..
Paid 106/each shipped - will sell $80/each shipped.