Agree with you @conn that what you request makes 100% sense and I don't see the use case for this "feature/oversight" neither. Don't have the Audio Pro but long time Sonos (Ones) stereo pair user. 
Maybe try to make the use cases and expectations clear between 2 different speakers in few scenarios. My understanding of what you report.
Use case 1: 2 speakers, 1 or 2 rooms, not stereo paired, not grouped: control each speaker volume separately both from app and physical buttons. Working OK.
Use case 2: 2 speakers, 1 or 2 rooms, not stereo paired, grouped: control each speaker volume separately both from app and physical buttons. Working OK.
Use case 3: 2 speakers, 1 room, stereo paired so it should become seen as a single speaker, potentially grouped with other speakers but irrelevant: control speaker volume stereo paired speaker set as one from app working OK but physical buttons still only adjust volume on a single channel. Definitely NOK.
				
			Maybe try to make the use cases and expectations clear between 2 different speakers in few scenarios. My understanding of what you report.
Use case 1: 2 speakers, 1 or 2 rooms, not stereo paired, not grouped: control each speaker volume separately both from app and physical buttons. Working OK.
Use case 2: 2 speakers, 1 or 2 rooms, not stereo paired, grouped: control each speaker volume separately both from app and physical buttons. Working OK.
Use case 3: 2 speakers, 1 room, stereo paired so it should become seen as a single speaker, potentially grouped with other speakers but irrelevant: control speaker volume stereo paired speaker set as one from app working OK but physical buttons still only adjust volume on a single channel. Definitely NOK.
 
				 
						 
 
		 
 
		

 .  One could argue that there a continuum between stagnant non-functional support and non-functional ever-changing software.  AudioPro is definitely on the one end, pursing a strong and simple approach to their products, at the risk of losing out on attractive features.  WiiM is squarely at the other end with constant tweaking in pursuit of more and better features, at the risk of making something weak and complicated.
.  One could argue that there a continuum between stagnant non-functional support and non-functional ever-changing software.  AudioPro is definitely on the one end, pursing a strong and simple approach to their products, at the risk of losing out on attractive features.  WiiM is squarely at the other end with constant tweaking in pursuit of more and better features, at the risk of making something weak and complicated. 
 
		