That’s a Surface Dial for controlling Roon with @DrCWO’s RooDial extension. While it is a controller for Roon, it controls the volume on the LSX’s when other sources are playing as well. 
My employer issued a round of new MacBooks, so I’m M1 MBP at the moment. Still on the fence about the beast that is the new iPad Pro (16GB/2TB anyone?) – but the dichotomy between hard- and software is holding me back. Maybe iPadOS 15 will offer a few surprises to pull me back in again… 