I have a solution. My old V6 TV box was replaced with a new 360 one 3 weeks ago. I have a Sony TV and a Sony sound bar, and no problem with the previous V6 set-up. When the new 360 box was connected we got the annoying sound switching between the sound bar to the TV speakers and back again. I tried changing cabling and settings, with advice from the Community site, but nothing worked until I saw a solution in another thread. The solution is to buy a HDMI CEC-less adapter and fit this to the end of your HDMI cable that connects the 360 box into the TV. This disconnects (terminates) the pin/ wire in the HDMI cable that the 360 box uses to control other connected equipment, and causes the unwanted sound switching. It isn't needed as the single control can be done directly from the handheld remote, like the old V6 one.
I know that Virgin Media should be doing this, but the adapter is cheap and saves a lot of angst to fit it yourself. It costs £11.17 from Amazon and it's a Lindy HDMI CEC-less (female/ male) adapter. It worked straight away for me and I've had no unwanted switching for 3 days now.
