the problem is that they're not uniformly thick -- the ends are much wider than the center, creating an uneven weight distribution that just happens to put half the monitor's weight right on top of the disc drive. if you can get a piece of wood, rigid plastic, or some other sheet of strong material, you could put it on top of the xbox and then put the monitor on that so that the pressure is moved to the corners of the case, which should be fairly sturdy. ideally the plank itself would be resting on something other than the xbox, but it should get you out of a pickle