I have a PS3 that

Question

I have a PS3 that I'm having an optical cable problem with. I have a KEF home theatre system, which i have connected to the PS3 via an optical cable. This works fine on the menu system and when watching a blu-ray film, but I have no sound when I load a game. I also have an Xbox 360 with the exact same set up and it works fine. there is light coming out the optical cable from both ends when plugged to the PS3. Please help me out. :)