Antennas will only work on devices that have a TV tuner. No Roku player has one. A Roku TV, yes, but no Roku player or soundbar.
The Streambar has no video inputs, so you can't connect a DVD/Blu Ray player. Same with the Roku Smart Soundbar. Other video devices would have to connect to the TV directly, and the audio would go from the TV back to the Streambar via ARC. It does have an optical audio input, in case your TV does not support ARC.
Dan Roku Stick (3600), Ultra (4640), Ultra (4670), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.