HI and welcome to Beoworld!
I do have BC6000s but am still on a traditional analogue connection via PlusNet, hence no experience of VOIP – yet!
However, assuming that the cable between the phone (little 3-way junction box) and the router is an RJ11 to RJ11, have you experimented with an RJ11 ‘crossover’ cable rather than a ‘straight through’ connection? (or vice versa if you are already using a crossover.) This has fixed a similar problem for me in the past.
It’s worth a try. And I think we are going to get more and more of these questions in the future as UK goes digital!
Your alternative is to choose a different VOIP provider, use a stand-alone analogue-to-VOIP adaptor and just use Virgin as the broadband ‘bearer’ – the third party adaptor would simply connect to one of your router’s RJ45 sockets.