If the Roku Streambar is connected via an HDMI/ARC port, then the TV output should be going through the Streambar. You have to ensure your TV sound settings are using the external sound bar, as it would any other sound bar.
If there is no HDMI/ARC port, the Optical output would be how to connect it. Again, check the TV settings to direct to a sound bar.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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