AirPlay 2 is limited to 44.1 kHz sampling rate. If you're trying to playback a higher resolution stream, it will be resampled to match.
However, the Hegel supports another protocol that will perform high-res playback - UPnP / DLNA. You need to use an app that supports this feature. On iOS, I use mConnect Player HD. On my Android phone, I use BubbleUPnP. Unfortunately, neither supports Apple Music so if you're planning on sticking with that service, it's best to use your iPhone and AirPlay.
There's no advantage to using a wired Ethernet connection vs Wi-Fi. As long as you're not hearing dropouts or glitches during playback then your network is performing fine. I have a Mac Mini on a mesh node that functions as a streamer / file server for a second system without any issues. I also pull the music files over the wireless backhaul to a Raspberry Pi 4 running moOde for the main basement system and it works perfectly.
Streamers, whether they're standalone or built into an amp, are just tiny computers - usually running some form of Linux. If you don't hear any obvious problems, then it's functioning as intended.