Airplay has always been high quality as it can and will resample to match the clock of sender to clock of receiver under the hood so Roon never class it as lossless. Also Apple TV resamples all content to 48/24 under the hood. It has nothing to do with AAC. Airplay 2 isn’t AAC by default you are miss informed here. Airplay 2 has two streaming options legacy streaming (ALAC 44.1/16) and low latency streaming (AAC256). It’s wholly app dependant as to which it uses and is decided by the developer. As Airplay2 added multiroom it adds greater stress to iOS devices to stream multiple lossless streams over its tiny Wifi chip and can result in dropouts in certain environments. Low latency is there to offer a more stable WiFi multiroom experience from iPhones and iPads as source. Apple Music uses low latency streaming. Roon doesn’t use low latency as it manages the streams not the iDevice it uses legacy so is ALAC 44.1/16. Qobuz app also uses legacy streaming for Airplay 2.