I've been trying for quite a while to get a PCI option ROM to load when embedded into the latest BIOS for this board.
The PCI IDs are fine, it just refuses to boot any of the ROMs I've tried. (iPXE, and the real bootrom for an 8169 NIC)

Unless it is loading the ROMs, but they just aren't being executed somehow.
I tried disabling all disk drives in the BIOS except for the network boot option and it still just says "DISK BOOT ERROR".

Any thoughts on how to debug this further?

Update:
I don't think the ROM is being initialized at all.
My theory is that if it had been run it would've hooked int 19h or int 18h but unless my method is wrong it doesn't seem to have been run.

Test:
Two files used for booting, just 2 simple files containing:
0xCD 0x19
0xCD 0x18

Shouldn't that have called the original PXE ROM I embedded had it run and hooked the interrupt?