Hi, we have a LG UHD TV 4K, model # 55UH615A-UC and would like to hook it up to our older Technics stereo system which has RCA jacks. I used the audio stereo jacks from the TV to the stereo but it does not work. There is not a head phone jack to plug in from the TV to the stereo either only a SVC jack and I take it that's for a service jack to analyze the TV? There is a Optical Digital Audio Out, so is there a cord I could use from there to the RCA jacks? Thank you for the input.