I have a 55" Samsung NU6900 that is a few weeks old. We tried to hook it up to our surround sound stereo receiver today via optical. The TV does not output in Dolby 5.1. The cable is plugged in securely. The display on the stereo will say "Dolby 3/2.1" until we press play on a show, then the display says "Dolby 2/0." This happens no matter what streaming app we use on the TV. The TV is set to output to the stereo, not through the tv speaker. In Expert Settings, Dolby Digital is selected. This doesn't make any sense - this stereo works fine with our Xbox One (we have the original Xbox One, which doesn't support 4k - so right now we can either have 4k or Dolby 5.1 and it is inconvenient).
I'm sorry to hear that, have you tried hooking the device to the soundbar then from the soundbar to the TV via HDMI?