I am not roku employee, and the majority of posters aren't either. I don't know what inputs and outputs you have on your tv. Just that your old Roku stick didn't need audio out like your new Roku streambar needs. And I guess your aftermarket headphones needs a audio output as well. But you usually only have one.
Edmund Roku Community Streaming Expert
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I have tried using an optical audio line splitter (which I presume is the ycable solution suggested). I connected the Roku stream bar to the TV by regular HDMI (not ARC), then connected the line splitter to my TV's optical audio out socket, running one line from it to the Roku unit and the other line into my Sennheiser transmitter. Still no sound to the headphones. This is why I have come to the conclusion that there is no audio going in to the TV - thus there is no way of connecting the headphones to it.
If this is right, the Roku streambar retains the sound signal - and since there is no port on it that would allow output to the Sennheiser, the problem appears insurmountable.
actually, if you have the streambar, you can't, but you can if you have a roku device that has no speaker. used to listen thru tv speaker and blue tooth headphones while using roku but can no longer since "upgrading" to the streambar. i agree that it's a disservice to hearing impaired individuals that there's no work-around with roku sound bars. i, too, purchased the streambar and hoped to use headphones through the app while others use just the streambar. i am extremely disappointed with my streambar and headphone use, but am now stuck with it. i've gone back to my older roku device and tv speakers which work fine with headphones!