not entirely sure what you mean here so will just ramble...
afaik skyhd does not support dolby digital over hdmi so you need an optical digital cable to run between your box and your surround system.
also, you need to set your box to output dolby digital - services then option 4 then 2 then change audio output from pcm to dolby d, save settings.
thats all i can think of at the mo really, if this doesnt help post back with the message you get.