DMZ! Really?
IMO connecting anything to a DMZ should only be done as a last resort, and is a bad idea even then.
For a console it's not that bad years ago I had sky and I did it with no harm at all.
How is configured at the moment? If you aren't using UPnP start by trying it.
Who said anything about a console? Either way the relevant question is how is the device (be it console or PC) connected to the hub? It would be unusual for a SR102 to default to strict NAT from personal experience.
Any chance the PC and Xbox are fighting over the same ports?