with regards to the sky box have you got scart to the tv and then separate phonos (red/white)coming from sky box to surround ?

I dont have sky (I have virgin) and my V+ box is wired surround to tv via hdmi and phonos (red/white) from surround to V+ box so same as yours and works fine.

Have you tried using red/white/yellow phonos to tv/sky from surround? try surround to tv via yellow (usually ext3) and red/white to sky and see if that works

hth