We appreciate you for sharing your interest regarding the Roku Stream bar. The Roku Stream bar has its built-in Roku operating system same as a Roku streaming player. In addition to that. Roku Stream bar is a powerful 2-in-1 upgrade with 4K streaming and premium sound for any TV. Hear every detail as you stream your favorite entertainment in brilliant picture quality with crisp, clear dialogue. You’ll be amazed at how something so small can fill your room with sound. Setup is simple with everything you need in the box.
For more information regarding this device, refer to the official Roku website at this link: Roku® Streambar®
Since they both run the same operating system, you may use your Roku 3 and Streambar individually. When you connect your Roku Streambar to your TV, the images you view there are identical to those on your Roku 3. It won't function if you connect the two. Furthermore, to answer your question, using the Roku Streambar will improve the sound feature on your TV when you are streaming.