GPU PassThrough in QEMU/KVM

Say…

I have 2 GPUs: RTX 2080Ti & GTX780. I want to pass-through the 780 to a Qemu Linux guest. The Linux guest is built from BLFS. Manually unbinding the 780 from the host causes the command to hang using either “pci_stub” or “vfio_pci”.

The fact that this is a costumed-built OS from BLFS makes any difference? Should I use another tool like QXL/Spice, OVMF, Libvirt? Also, I came across a thread that suggested flashing the GPU bios.

Thanks,
KeepnItReal