I’ll wait for your tests, but quickly, “need more info” ^^
Which method ?
Dunno what you mean exactly (but boom not fun ^^).
Yeah I don’t know if it’s supported, and my passthrough tests are quite old as I never had problems since, but IIRC I’ve found it easier (read less error prone) to bind to pciback early. I had more problems using the usual recommended method to bind devices via modprobe, and use the kernel way since (well in fact I use a rather unusual method since, but I don’t know how to make it work on Qubes/fedora yet).
But in your case it may render your system unbootable, don’t know.