Does the virgin V6 box have native 2160p setting for UHD content on the box? If the box is doing UHD content then it might be best to leave it at 2160p. Otherwise you would have to keep switching the V6 box dependent on content which is not ideal.

With my Youview box its easier as there is no 2160p so its easier. to leave it 1080p and just let the TV upscale.