I've tried numerous ones in the past, they all worked fine and that was with sky +. However the problem I encountered was interference from my wireless router as they are all 2.4ghz, as most senders only have 4 channels to choose from, couldn't find a channel that didn't suffer from interference so gave up in the end.
Don't know much about the virgin boxes, how many outputs are there? Sky boxes have 2 rf's out, does the virgin box? Depending on the distance involved and if a scart cable is involved you can use a splitter asnd run a scart to both tv's.