Try hooking it up using Connection #11 on the below diagram.
I have a soundbar that I have tried setting up to my Samsung UN55B8000 55" LED via the red/white audio cable. I hook it up to the back of the TV, go into the SOUND menu and select 'External Speaker' - but I hear nothing.
If I hook up the soundbar to my Samsung BDP-4600 the soundbar works fine and I hear sound.
I want it to work with the TV - what am I doing wrong? Thank you in advance!