Sorry I can't be more specific as I don't have the home cinema sytem, but you will need to connect your sky box to the audio system using the toslink cable that you have, it may have to go into the back of the dvd player that comes with the system?

You might also need to select the correct channel through the system when watching sky, so the tv picture will be from HDMI 2 (for example) and the sound will be through the optical...