@l1c I got it to work. But not in that HP G6 server.
I have an identical ML350 G6 and its working fine with same version of XCP-NG.
Only difference is there are less pci cards in the machine. This goes back to my original idea, because other cards share the same IRQ the pass-through becomes for difficult.
Any configuration suggestions? Is there a way to edit the IOMMU groups?