Brink, your infinite wisdom; I call upon

I have this sound system:
LG Home Cinema System | HT303SU : LG UK
As I am in the UK, not everything is broadcast in 5.1 surround sound. Because of this, as i watch tele, I only end up with the 2.1 surround sound, and my rear speakers not being used. It's connected to the tele through SCART as I haven't received my HDTV yet; next Saturday.
I was wondering if there is an option somewhere that make it always use all 6 speakers or will this change when I receive my HDTV?
It doesn't have an optical connection, but it does have SPDIF I believe. What is this, and is it related to optical ?
Thanks in advance buddy

Oliver