I don't have the virgin STB you mention though this may help as a first step.
Set the STB controller to permanently on or always on. That way the box should never turn off. Turn off both the Avant and the Virgin media box then turn them off at the power point for about 10mins. Then turn both on. Try the Beo4...
In my case the Foxtel and PVR boxes seemed to get out of sync and this process 1; rectified it then 2, ensured the STB always stayed on 3, problem solved (in my case).
It may also be worth trying the red button on the beo4 as it send an on signal in some STB's are in sleep mode of off and also placing a section of opaque tape over the ir transmitter.
Hope it helps, beoaus