Airplay doesn't transport audio files, it transports an audio stream that has been decoded from your audio file by the originating audio player application.
The audio player application decodes the given file into uncompressed audio data and hands that uncompressed stream of audio off to the operating system. Dozens of different things can happen after that point, however. And what exactly that will be is entirely up to the audio APIs that the audio player app is programmed around, how the audio pipeline on your Mac is set up, the macOS version that's in use, what third party applications you give permission to interfere with that pipeline, and how they in turn were implemented.
That's precisely why I, personally, am not a fan of third party audio pipeline applications like Airfoil, Loopback, Audio Hijack, SoundSource, et alia. Understanding the path your audio takes on any operating system is already a bit of a nightmare in the best of cases. Adding any more or less entirely opaque third party applications to that mix only complicates this without actually offering any actual benefit beyond some edge cases that some people insist on wanting to have covered.
Even solid state, mine would be going into a 14 tube amp so I could certainly get by. Tube phono preamps can be very sensitive, I cannot get my phone anywhere near one I am using now.
