if u unplugged one of the speakers may be sound back. or u removed the Dell speakers altogether and routed the sound out of the tv and through stereo. There is and audio out on the back of the tv that should connect with connector cables into any stereo/mixer.
may be the head phone jack just plug in some headphones into the TV, and try if sound come out.
Check Sound and Audio Devices Properties in Audio tab,and make some change their