Apps like offer massive libraries of movies for free. While much of their older content is in stereo, many of their modern action and sci-fi titles support Dolby Digital 5.1. 2. Digital Libraries and Archive.org

Dolby Digital 5.1 is the industry standard for surround sound. The "5.1" refers to the channel configuration:

Use an HDMI cable rather than an Optical (Toslink) cable if you plan to move up to uncompressed formats like Dolby Atmos in the future. Conclusion

The Subwoofer (for deep bass and cinematic "thump").