While almost on the verge of giving up I'd like to share succes with the above hardware.

Biggest change was using i1440fx-4.1 instead of Q35-4.1!

 

With the help of you fellow unraiders I am using the following syslinux configuration while booting unraid:

append vfio-pci.ids=10de:21c4,10de:1aeb,10de:1aec,10de:1aed isolcpus=1-11,13-23 initrd=/bzroot video=efifb:off

 

vfio-pci.ids=10de:21c4,10de:1aeb,10de:1aec,10de:1aed     to not have unraid use them (videocard, sound plus a few other things, in fact the entire IOMMU group)

isolcpus=1-11,13-23     to allow unraid only using cpus 0 and 12 (which it prefers and thus the rest really for VMs and Dockers)

video=efifb:off     another parameter to avoid video (card) conflicts.

 

Obviously isolcpus=1-11,13-23 is optional.

 

Spend a lot of time using the Q35-4.1 machine. And actually, once I was able to also install the NVidia drivers, replacing the Microsoft Basic Display drivers, but thereafter could never get the VM to boot properly. And then going back to VNC even messed up the MOBO BIOS.

 

Then tried the i1440fx-4.1 machine, basically as a quick test.

 

ET VOILA, Windows on Screen (instead of black screen or nothing at all).

 

Passing through the videocard (also) using Graphics ROM BIOS for my specific card downloaded from TechpowerUp.

 

Hope this helps.

Good luck.

 

This is very similar to my build. Can I ask, were you able to get Hyper-V enabled in Windows 10 (or is it not something you even use so you don't care)?