I am playing Spotify - casting from an iPad to the Port. The port is connect to my Onkyo via analog ¼ in cables.   I can’t control the volume from the receiver nor from the Sonos app .  It says if is controlled through Sonos.  So do I just accept whatever volume it decides to play ?    

The useless  fixed, variable and pass-through settings on the Sonos app seem to have vanished.  I’m not quite sure what the “ expected” behavior is supposed go be - but this is an ongoing issue that only seems to be getting worse!