I'm looking for help and suggestions with problems streaming to XBoxes.

I have a PP and 2 XBox 360's on a home network built round a powerline 'backbone'

I have a adsl router in one location connected to the powerline network. The PP is upstairs connected to a hub which in turn is connected to the powerline network. Xbox 1 is likewise connected via a hub to the network. XBox 2 is directly connected to the powerline network.

The PP has been on and undisturbed (no resets or file changes) for days and has the 2.5.6 firmware. 

XB2 works great. It sees the PP and streams media well with no problems.

XB1 doesn't. It now lists the PP as a source in the 'Select Source' page but when I select it the 'spinner' just spins for a long time and then reports back that th XB cant connect to the 'PC' with the suggestion that a firewall may be blocking the connection.

If I perform the network test then I lose the PP from the list of sources and 'no computers found' is displayed. A reboot of the XB doesn't normally help in either case. Sometimes the PP will reappear as a source but I've not yet discovered what causes that to happen.

I've removed the hub from XB1 and direct connected it to make the setup identical in both boxes - no change.

The only other difference in setup is that the adsl router has a rule to make XB1 the network's DMZ.

Does anyone have similar problems with more than one media extender? Can someone explain the processes that go on for connection/discovery so that I might do some more troubleshooting? 

Thanks.