Welcome to the Roku Community, @415Kirk!
Thanks for reaching out. We'd be happy to provide further information about this.
The remote for Roku devices is designed to manage the TV's volume and power. The TV, equipped with HDMI-CEC, is responsible for controlling the Soundbar. Therefore, for the Soundbar to be appropriately controlled, it must be connected to the TV using an HDMI cable.
For reference, you may visit our support article dedicated to this: How to set up your Roku voice remote to control your TV
I hope you find this information helpful.
Best regards,
Carly
Carly Y.
Roku Community Moderator