So I have gone through part three of the guide (here and also here) and have made sure that everything relating to the hardware passthrough of the video card and the USB card are correct. And they are. It is set up exactly how it should be.
I checked that both the video card and the USB card are being assigned the vfio driver, and for sure the video card is. The USB card, for some reason, is showing that the driver in use is 'xhci-hcd.' Not sure why that is. It is set up identical to the video card. I removed the USB card from the VM settings just to see if that helped. It didn't.
At boot I get four errors relating to ACPI:
ACPI Error: [\_SB_.PCI0.XHC_.RHUB.HS11] Namespace lookup failure, AE_NOT_FOUND (20160831/dswload-210)
ACPI Exception: AE_NOT_FOUND, During name lookup/catalog (20160831/psobject-227)
ACPI Exception: AE_NOT_FOUND, (SSDT:xh_rvp08) while loading table (20160831/tbxfload-228)
ACPI Error: 1 table load failures, 8 successful (20160831/tbxfload-246)
This shows up right after selecting the kernel to boot. I have no idea if this is relevant.
So, yeah. I have no idea where to go from here. It just doesn't work.