Where is the manual that came with your sub? If self powered it needs an audio input usually on a red or white cable. Yellow is usually reserved for video signal.
There are no audio outs on your TV The digital audio out is an optical output meant for a sound bar or a stereo audio amplifier that has an optical input. If you have a compatible stereo system you can use an optic cable to connect the two and then use the headphone jack on the stereo system.