My use case is that I wanted WiiM Ultra for my office setup, so below I will describe how I am using it and how those things work.
Amazon Music Streaming
As a side feature, I have an Amazon Show in my office and it can control what is playing in the Ultra with Alexa voice commands. Also, the included remote has Alexa built in.
Airplay
I don’t plan to use it with AirPlay very often, but I dug through some drawers and found my old AirPort Express and connected it to the optical input. It does AirPlay 1, which I prefer to Apple Music to AirPlay 2 in this setup. In short, AirPlay 1 is lossless up to 24/48 with Apple Music and AirPlay 2 is lossy 256k files with Apple Music.
As a side note, if you have another Wiim device, you could connect it directly to the Ultra or you could Airplay to the other device (if it is in another system) and then link them in the Wiim app and get Airplay to the Ultra that way.
RCA Line In
Phono Input
DLNA
As a side note, you can use the meter with inputs that have album art, as well.
I also tested the Home Server link built into the Wiim app. It connected to my Plex and LMS servers without issue.
Chromecast
The Remote
Headphone out
The Wrap Up
Extra: I did mentioned multi-room linking in the Airplay section above, but one thing to be considered is that when you feed phono or a line input into the Wiim Ultra, you can now share it with other Wiim devices in the house. It is pretty cool to listen to vinyl in rooms without a turntable. Of course, you still have to get up and go in the other room to flip the record, but it is what it is.