I have my hummy connected via hdmi to LG F7700 tv. When I use hummy's optical out into amplifier playing the bbc hd test card gives me all 6 channels. When I use the tv's optical out it just gives me 3 channels. I assumed that hdmi would carry the dolby signal to the tv and then via the optical output into amplifier. Is that not so? Could I have the wrong settings on my hummy and/or tv?