I've just got my suuround system from Argos, got it home, plugeed it in and.....fuck all

Anyway I'm taking the processor back 2moro but in the mean time I'd like to put the speakers where I want them but theres no feckin instructions in there!

Does anyone know what position they should be in? I've got:

Surround left
Surround right
Main right
Main left
Centre

I know where the centre goes lol