Kent bought a sound bar for his older Samsung TV. He uses a Chromecast and Roku Stick with it, but he can't get audio to work. Scott Wilkinson says that the optical out for the old Samsung is probably only for the TV's internal tuner since it's older than the advent of streaming media. There could be a setting in the menus, but he's better off going with HDMI input.
The bottom line is that he'll need to either upgrade his TV or get an AV receiver that will be able to take all the TV sources and route the audio properly. Getting a receiver would be much cheaper than a new TV. Kent can get a really good receiver for under $500. Denon is a good place to start.