$$$ Decked out Motherboard:
X10DRH-CT = Works with all NVME I've tried.
From Super micro:
Checked with our LAB and verify with BIOS engineer. X10DRI did not supportAOC-SGL3-2E4R card.
X10DRW-I and X10DRL-CT, X10DRU motherboard did support AOC-SGL3-2E4R card.
According to BIOS engineer, X10DRH motherboard did support AOC-SGL3-2E4R card.
The X10DRH is a badass motherboard but is not cheap. X10DRH-I is way cheaper than the -CT that I have, so that may be the best way to go.
Or, if you don't need AICs that other NVME motherboard is waht I'd buy, it's in my cart/list on a couple sites.... onboard NVME + NVME AOC are short so that shuold work, I was concerend about the HBA, and other longer cards though :/