However, the system freezes when the card is enabled during the time the OptionROM should be posting to spin-up, inspect the drives, etc.
Tried CSM Enabled/Disabled (UEFI), Legacy Only, UEFI Only, Legacy + UEFI, UEFI + Legacy, etc.
It just flashes a cursor, which tells me the OptionROM isn't initializing.
However, to get the system to boot I have to set either the Storage to UEFI (which skips the optionrom for this card), or disable CSM all together. When doing this, I cannot see the PCIe device for the card - which tells me, it isn't initialized! Doh!
Nevermind! Turned out, forcing it to UEFI actually did work! Shows up under lspci and drives now show. Woohoo!