I am running NVIDIA P40s on a DELL R720/R730 and a NVIDIA A2000 12GB on a DELL Optiplex 9010 in my playlab. Getting the GPUs to be accessible for VMs was quite easy: shutdown the XCP-ng host, install the GPUs, start the host again, activate the GPU in the advanced settings of the host in the PCI Devices section (“Passthrough enabled”). The host will restart at this point after displaying a warning. That's it – the GPU can now be assigned to a VM in the VMs advanced settings. I do use the GPUs for AI workloads under Debian though, so your use case might vary.