This is a tricky question, as Dolby Atmos capabilities and its actual output are two different things. The thing that makes Atmos distinctive is height channels, an innovation over Dolby Surround. Strictly speaking, the bare minimum to enable Atmos sound is 3.1.2, meaning a left, right, and center channel as the main sources of sound, with a subwoofer for bass and two Atmos-enabled speakers for surround. However, this setup will condense a lot of channels together. Typically, it’s recommended to have a seven-channel surround system, a subwoofer, and four Atmos channels (7.1.4) to avoid folding too many sound objects onto and into one another, but a truly ambitious person can go all the way up to 24.1.10 if they have the money and space for that many speakers.