Best answer by Airgetlam
Those red and white RCA outputs on your TV are analog, you'd want to be taking the analog signal, and converting it to digital (optical) which would then feed the PLAYBAR.
And in all honesty, if I was you, I'd be pulling the audio out before it reached the TV, not after. Using an HDMI switch with an optical output on it, something along the lines of
That way, you would be getting the full Dolby Digital signal going to your PLAYBAR, rather than the stereo signal that the TV is processing.