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The Sonos Port functions as a Sonos ‘speaker’ except with a line out and a line in, instead of a speaker. The line out would be in sync with any other Sonos speaker and external system’s speaker as well, assuming the external device is not adding a delay itself. The analog input would delay the signal by 75ms in order to buffer enough data to play in sync across any connected Sonos device, so it would not play well with non-Sonos speakers.