This article and subsequent conversation about AirPlay 2 is about a year old but should answer your question:
https://audiophilestyle.com/ca/contributors/what-airplay-2-means-for-your-listening-setup-r717/#comments
The take-away is AirPlay 2 converts everything (audio) to ALAC and is bit-perfect at 16/44.1. All high res files are re-sampled to 16/44.1. In the end, it depends on the capability of the receiving device (your MX122) for bit-perfect play of the stream.
https://audiophilestyle.com/ca/contributors/what-airplay-2-means-for-your-listening-setup-r717/#comments
The take-away is AirPlay 2 converts everything (audio) to ALAC and is bit-perfect at 16/44.1. All high res files are re-sampled to 16/44.1. In the end, it depends on the capability of the receiving device (your MX122) for bit-perfect play of the stream.