At $349 each, you’ll pay a pretty price to get two HomePods and pair them to work as stereo speakers. The stereo feature relies on AirPlay 2, which Apple pushed out to iOS, Apple TV, and HomePod in May 2018, after a long delay.
You’ll note I didn’t list macOS. That’s related to the question I received from Macworld reader Mikael. He paired his two HomePods for stereo sound, and cannot figure out how to access them from macOS as a single stereo audio destination. The reason? It’s currently not possible. (See Apple’s system requirements list for AirPlay 2.)