You will need to call Virgin Medai C/S to discuss this, but before you do...
Are you asking about replacing your single TiVo with a single V6? If so - be sure you have VM broadband (for this is a requirement), and take a look over the new bundles on the VM website (try https://store.virginmedia.com/build-your-bundle to get an idea of pricing - although be aware of "new customer" discounts vs standard prices) to have an idea of what packages are available. You will probably be negotiating to move to a new TV package and re-contract for 12/18months in return for the box-swap and possibly a discount.
Or are you asking about adding a multiroom subscription, and having more than one box in the house? Some sections of the VM website will give some prices for this, but I wouldn't place bets on those being accurate and this can very often depend on your bundle & package.
If it's a straight box-swap, this can often be done via self-serve "Quick Start" - if you want additional coax points installed for additional boxes, this will require an engineer visit.
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