You set the TV to use optical but for reasons I can't guess some apps have their own sound menu for you to set. As there is no standard I find myself looking through the app's menu about sound.
If there is no sound, be sure to set the TV and apps to only send Stereo or PCM. Some receivers are silent when you send other audio formats.
I recently got a Samsung SMART TV (MU6300). Currently do not have cable so the only thing I need hooked up is the sound so I can play Netflix/Amazon Video/Youtube via the TV. I have 2 external speakers connected to a Pioneer receiver. I have a turntable also connected to the receiver which plays sound just fine.
I've tried connecting the TV via the ARC to the Receiver (which the TV detects but no sound is coming out - I went into the audio settings on the TV and changed it to HDMI sound.)
I've also tried connecting the TV by optical cable to the receiver and then set the audio to optical on the TV, still no sound.
The receiver in both instances were on TV mode..also tried it in several other modes to no avail.
Anybody have a solution? Pulling out my hair on this one.