This is going to be a long article, but if you want to skip ahead, I will have different titles for specific features. I am going to start with Hi Res since that is the one that really sets this product apart. However, I will move into other features that were pretty awesome before the latest Hi Res update.
Note: I may get paid commissions for purchases made through any links to Amazon products on this page. Also, I get some products for free to review from Amazon (though, I do have to pay taxes on them).
Hi Res Audio for a C Note (or less)
Qobuz and UPNP
Amazon's Music Service is available in their app, though. You can even use an Echo device to control what is playing on the WiiM by voice if you have Amazon Music and an Echo. I tested it with Apple Music, which works on the Echo, but it says "Apple Music is not supported on this device". When you use the voice features on the Echo, I believe it uses Bluetooth to send the signal. In any event, you will get a 44.1 signal using this method.
Airplay 2 and Apple Music
One of the upsides to using Airplay with Apple Music is that it can be controlled with Siri (once you add WiiM to the Home App). This can be controlled via the iPhone (Apple Watch), HomePod, iPad, and MacOS. This also allows for easy multi-room control.
Note (3/4/22) - I asked WiiM about the Airplay issue and they have resubmitted their app to Apple to get Airplay to use 44.1 rather than 48k. I will update when I see that update come through.
Bluetooth and other stuff
The Wrap Up
Hi Res Output with certain applications (mentioned in article)
Bit Rate Switching on the fly
WiiM only supports Qobuz service for Hi Res natively as of today
Would love a USB audio output