Connect HomePod to iTunes Library

My computers, Windows and Mac, can both play to my HomePods, although only iTunes on Mac or my iOS devices work properly with the stereo pair. If you're having trouble playing to HomePod from a computer take a look at If you can't use AirPlay or mirror your device's screen - Apple Support.

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You need to set the Homepod(s) as output from iTunes on a Mac. Then use iTunes on that Mac to play music from your library.

Homepods don't work with Homesharing like Apple TVs and so cannot directly access your iTunes library. They can work with Apple cloud music services which may mirror your iTunes library - see the discussions on this forum.

Using stereo Homepos is even more restricting - Mac apps other than iTunes wont see them.

... and then even when they see them, most often iTunes cannot play on them...

Only work-around I found is using your iOS device as an intermediary : access your music library from within an app on your iOS device, and connect the audio output of the iOS devices with your HomePod(s). Apple should clearly work on MacOS solutions. But such is no priority for them, I have the impression. iOS is.