well what are you connecting it too? 2 channel? 4 channel? 5 channel or more?
Front line out is the normal steroe
Rear is the rear stereo
third had the centre and subwoofer
IDepending on what you are connecting too you need to change the outputs fromt he soundcard.
EG 2 channel amp: use 2 channel stereo mode and jsut connect the front stereo connectors.