I have a Sonus Port hooked up to a vintage amp and a stereo pair of Era:100 speakers elsewhere in the house; all is working fine.
There's an old unused iMac in the house running OSX Sierra 10.12.6 (it won't update beyond that) and I can see the rooms with Sonos gear under the iMac's speaker options (Internal Speakers, Kitchen, Living Room).
I haven't been able to get iMac sound through the Era pair ("Kitchen") nor the Port ("Living Room") whether that's local audio files, or a webstream (Internet Archive; BBC sounds).
I have installed iTunes and the sample library file doesn't play to the Sonos gear either.
Everything on the iMac plays through its internal speakers.
I'd be grateful for any suggestions for any tweaks or configuration settings that might allow me to get the iMac running as a Sonos interface -- essentially a Spotify player -- as an alternative to the Sonos app for sig oth.