Just got sky + hd installed today. I have hdmi and optical connected from sky box to amp and i'm only getting 3.1 surround sound.But when i connect hdmi to tv and optical to amp i am getting 5.1 surround sound. Trying to watch transformers on sky hd. Do I have to change some settings on the amp and how do i do this? It seems that hdmi is taking priority on sound input to amp.