to the forum.
As far as I am aware, You need to pay for a multiroom subscription if you are going to use more than one box as VM's security requires that each card be paired with the box it is used in. It also requires that each box is only used in the building where it was registered.
If the cable is in place and in good condition, there would be nothing stopping you taking your VboxHD into the other room, although you'd obviously lose the ability to watch it in the living room at the same time.