Yeah sorry Andy. I misread your first post and then only partially fixed it with my edit.
However as Bob says, and shown by changing the settings fixing the issue, you are still using DLNA to push media to your living room client. It would be better if you had a solution that used the MC's MediaServer protocol.
What I was trying to suggest, which I can't test as I don't have enough PCs here running MC, is that if you ran a MC Client on the laptop and then directed the Server 2008 R2 copy of MC to send media to the Living Room MC Client, you would probably be using the MC MediaServer capabilities instead of DLNA. It may require setting up more zones if you don't have them set up already, and indeed setting up MC on the laptop, with the Server and Living room devices set up. It would work sort of like Gizmo telling a MC Server to send media to a separate MC Client.
I'll leave it to Bob to confirm if that would work.
Using the MC MediaServer capabilities may help with the windowed mode issue as well, although I thought I saw a discussion and some settings somewhere to address that. I'll leave that also to Bob.