No, roku remotes only control tv volume. If you can get your tv controlling the volume of the soundbar via hdmi cec, then the roku remote will control the tv, which then controls your Sound bar.
I gave up on trying all the other "solutions." I have a Roku (series 6) TCL TV and a Sonos Playbar and Sub. I bought a device called the "Sideclick" which clips on to the left side of the Roku remote and gives the necessary IR signal to control the volume of the Sonos stuff. The TV remote is wi-fi (only-it seems).I still need the phone app (Android in my case) to adjust sub level, EQ, compression, etc.). To program the sideclick, I used a Samsung remote's volume buttons, which is learnable (or maybe the default) of the Sonos Playbar.
My situation might even be more odd. Same Roku IR setup and same soundbar. I had a Vizio TV and it all worked. Got a new TCL Android TV and now it won't. If I press the pairing button on the remote and start the setup process it works for vol up, vol down, but the roku remote has no mute. I even tried a work around I saw somewhere to use a second remote for the mute (which sonos picks up). But near the end of this the Roku box and remote auto-pair, and the sonos soundbar doesn't pick up the roku remote signal (no light flashing when the remote button is pushed). I'm flummoxed. Sidekick it is, I guess.
