My Mac running Sonoma will switch to AAC playback when connecting to my AirPlay 1 receiver
From my understanding, if it is an AirPlay 1 receiver, it can only accept ALAC. Even if the
playback is AAC, it will still get converted (upscaled) to ALAC for
transmission to the AirPlay 1 receiver.
I wouldn't be surprised if the right combination of AirPlay 2 hardware did allow lossless playback too.
Correct. Per the video: AirPlay 2 compatible hardware does not automatically force AirPlay 2. The app's developer can still set AirPlay 1 to be used - meaning ALAC 16-bit/44,1kHz.
Does anyone know if the "AirPlay Receiver" for mac outputs in Hires lossless (24/192)?
No matter the source quality or what the DAC of the receiving Mac is capable of, the AirPlay protocol for Macs and iDevices is limited to ALAC 16-bit/44,1kHz (48kHz).
HomePod seems to be an exception: Apparently it can stream up to 24-bit/48kHz to other HomePods.
If you force 24/192 on the DAC, this will be the output. But the data it receives via AirPlay is limited to 16/44,1 and will get upsampled.
Edit: The only way make use of HiRes lossless and the DAC is to directly connect it to your Mac/iPhone/iPad via USB/Lightning/30-pin.
If you use the
Remote.app for iOS/iPadOS you can
control the Mac's Music.app and play HiRes content.