excerpt from http://geekout.io/index_files/The_truth_about_AirPlay_audio_streams.html
AirPlay uses regular WiFi standards (802.11n) for transmission of audio and video content. Against initial speculation this process is not limited to Apples Airport station, third party routers equipped with this protocol can handle the streaming without complications. The only predisposition necessary is that all participating hardware is on the same WLAN network.
AudioMIDISetup
What is the audio quality for this type of transmission?
In contrast to Bluetooth connections, which sometimes lead to downsampling and loss of quality, AirPlay is transmitting “CD quality” audio (16bit / 44.1kHz). This can easily be verified with the Audio Midi Setup tool that is located in the Utilities folder in your app directory.
For streaming content Apple is using the in-house Apple Lossless Audio Codec (ALAC). Here data density is permitted for up to 120 megabit per second. No matter what format the audio originally coded, your Mac or iOS gadget will turn it into a lossless audio stream. Only so-called “Hi-Res” Audio formats used by pros and audiophiles with higher resolution (e.g. 24 Bit / 192kHz) will be down-sampled to 16 Bit / 44.1kHz.
Video playback with tricks
Video streaming is tricked out by Apple. Audio tracks in videos are generally sampled in 48kHz. The AirPlay specifications state that audio needs to be down-sampled to 44.1 kHz for remote playback. The subjective audio quality itself is only decreased minimally. Most of the video content available online is limited to 160 kBit/s transmission rate for audio. This also applies to movies and TV series on the iTunes Store. = = = = ==
given this input one can stream up to 16/44.1 from which ever service via Air Play... and now Air Play 2, into what ever is supported by license from apple, apps, hardware, etc.
check the audio midi app on your mac to see what is what in terms of available..
if the service however streams out at max MP3 levels or 320bits that will be what one realizes and no more.
I'm a bit at odds on things being upsample or rather converted into another format entirely to lossless as is said in the above article regardless if it comes from Apple or not.
despite the conversion, if any, one only gets what is there. no magical changes arise during conversion from lower bits of info via fidelity when one merely increases the size of the file from a condensed or compressed file.
only native rips into 16/44 will be unaffected if a format is converted, ala, WAV to AIF, or to FLAC and or ALAC. lossless to lossless.
this said, much depends on your ears and system as to wether or not you'll either detect some loss, or just enjoy what ever streaming rate you are receiving.
maybe its best to stay in the dark and just let your ears decide which service sounds better.
I've not connected up with TIDAL or 'boz but do have Apple Music and Spodofy. of these two the latter does often seem to present a more expansive stage. Yet fidelity seems to have little disparity between them, yay or nay. its IOW, a coin toss in terms of SQ between them.
even with my current feeble rig, listening to lossless vs lossy files is pretty readily realized, so opting for uncompressed streaming even with Air Play I or II ought to do well within its designed constraints.
Hope this helps.