and if you check that setting in AMIBCP you’ll see it has no enable/disable option. i have that same PCI Subsystem in dell laptop menu, but is not showing anything. also have another USB related setting that has no enable/disable option in AMIBCP and that feature seems broken as changing it in BIOS does not change any bit in NVRAM
flash your mod via external programmer and dump back to compare checksums, so you can be sure everything is written in place