What was that about Dave?
Anyone thinking of altering and flashing their logic boards boot rom should use extreme care, all the normal warnings apply, it could brick your Mac, burn your house down, kick your dog, or knock up your teenaged daughter.

Anyway, two completely different targets, obviously if you are dealing with an add on PCI card that has a ROM chip on it, it's best to just flash that rom chip with a Mac compatible firmware if the device needs to take part in the boot process. However what users have been doing is adding NVME booting to their Boot ROM, because we have no source of M.2 boards with a ROM chip, and I'm not aware any even exists.
There is the hope of the "Holy Grail" of getting cards with GOP roms working with cMPs, but it's just idle talk, no one is really actively working on it, and other than a few reports no one really knows how to do it, or if it will even work.