I have a lg tv (32lg30) connected to my lg home theater system LHB953 by an optical cable. When watching cable that supports 5.1 surround sound, it will not play on all 5 speakers. It only plays through the center speaker and the left and right speakers. When watching a dvd, the rear speakers are not playing nearly as loud as the center speaker. All the speaker levels are the same. Is there anything I need to change to get 5.1 surround sound through cable and increase the rear speakers?