In a screenshot shared by the same user, a menu page within the app does indeed provide details on adding a second subwoofer to a Sonos home theater setup, specifying that while the first Sub must be a Gen 3, the second must be a Gen 1, 2, or 3.

The Sub Mini, the page notes, is not currently supported.

The only problem with that is that Sonos hasn’t yet made any official announcement about the existence of the Sub Mini, making the freshly-spotted leak its unofficial internet debut.