I have recently added a wiim ultra to my ecosystem. My use case is two fold; firstly I use it as a headphone amp for Spotify, my NAS library and my turntable, because Sonos inexplicably has no option to integrate headphones (even the ones they make)
Second, for aforementioned turntable I use the wiim ultra to cast a flac stream via DLNA to my Sonos set up.
It works great, I chose a target speaker in the Wiim app for the stream and then group the additional speakers.
Except when I change the volume on the wiim it only affects the linked speakers, not the group. This means I have to use the Sonos app to control the group volume. Annoying
I have spoken to Sonos support who didn't really want to discuss as they state this "is not a recommended set up" (despite the fact they have no alternative recommendation for my use case(s)).
I have logged a feature request but thought I'd check here if I'm missing something or anyone has found a workaround...