You could go the low tech route of simply turning one pair off when not needed. I have installed many systems like this ( mainly in "L" shaped rooms, or "knock through" living / dining rooms)
Easy to do with powerlink supplying all speakers with L&R - just switch of the mains supply for the pair you don't want to hear.
You can "daisy chain" Beolabs - many have two sockets.
You can also get B&O made splitters, or you can just splice the PL cables ( care needed but easy and effective)
The only real drawback compared to a beolink is no different volume control is available for pair A and pair B when they are all on - but maybe not an issue in the room you describe.
Also, if you have a video source ( or some newer audio systyems) , link would offer the option of different content in pair A and B - but in a one room system, this would sound a bit odd!!!