I certainly have noticed different inputs have different volumes associated with them, I’m not sure I’d take the assumption that Sonos needs to adjust volume to each. Apple streams in particular seem to be different volumes between Atmos content and stereo content, and those are both different than Amazon music, as is the input from my Apple TV using Hulu. I adjust my system as appropriate, sometimes more than others. Personally, I don’t want yet another system trying to adjust volume by applying a filter for me,  

That makes sense. I have a 1/Beam, 2/couple of SL’s and a 3/ Play (as direct line for Vinyl) grouped together (along with a Sub), and the volume seems to randomly change across them when source is adjusted. I shift frequently between music streaming, tv and vinyl (line-in), and often times when the source changes one may even have the volume at zero, I’m forever needing to go the App to adjust. Is there maybe something basic I am missing in the way I have this setup?  

No, Sonos doesn’t offer any ‘line leveling’ across streams and inputs. My perception is they want everything to be as pure as it is handed to them. 

 I had that issue a while back when I was creating Sonos Playlists with a mix of my library music, Apple Music & Qobuz.  When I listened to these Sonos Playlists the Apple Music tracks were much louder than either my library tracks or the Qobuz tracks.  At that point I began to replace the Apple Music tracks with the same tracks from Qobuz.

Normally speaking , you might have been able to adjust the settings for each music file’s metadata, which often contains a 9’volume’, but that doesn’t work well with streamed music, since you don’t ‘own’ the file to adjust it.