Thanks for such a quick response. Wish Virgin had made that clear.
Unfortunately the oldest box isn't near the hub and is the only room in the house (a remote extension) without decent wifi so the TV6 cant be installed there. I could replace the oldest Tivo box (at the hub) with the TV6 it and then move that Tivo box to replace the oldest box but then I lose all my recordings. Might be best not to fit it at all. Unless Virgin has extenders that wok on the mains circuit, normal range extenders don't work into that room.