Scart will only ever carry stereo audio - the .1 part will be applied by tha amplifier/audio processor in the surround system.

Steve, it depends how you connect stuff to the surround system. Does it have auxiliary inputs? If so, which type? Twin RCA/phono? Optical Digital? Coaxial Digital? Likewise, what audio outputs does your Sky box have? Twin RCA/phono? Optical Digital? Coaxial Digital?

Another point worth noting - not all Sky - in fact very little - will be in 5.1 surround sound. So if it's not being broadcast in 5.1 surround sound, then the amp won't be being fed 5.1 surround sound. Unless the surround sound processor in the amp can run in pseudo-mode and "create" a multichannel audio output, like how Pro-Logic works in most amps...