As Barry suggests, some trial and error with your TV's sound settings is probably the best way forward. It might also be worth looking under Help & Settings > Settings > Audio on your Virgin set-top box to see if there's anything there which might help.
Ideally, you should be looking for the words 'normalize sound ' (or 'normalize audio') on either device. If that option's available, using it will bring the highs and lows of the volume range closer together. If it's not on either device though, just play around wit the sound settings that you've got until you find something close to your needs.