I stand corrected:

The Toslink cable provided by WIIM does work with 24bit - 192 kHz files.
Just tested it together with the two new short digital cables that arrived yesterday, no difference by performance except for my personal Bias for the shortest one of 50 cm. It's quite handy ;-)
Possible reason for my fail: Firmware update in the meantime or multiple human mismatch. Prefer the first option ;-)

However, it is important to underline that you won't need to add another cable to your WIIM, it seems to be sufficient if you only add an USB power socket or an USB power bank for supplying the current.

Re. Airplay2:
If you followed the discussion in the related thread, Airplay2 for Audio seems to be a trigger for Apple-Aficionados but technically not so overwhelming if you're not interested in Multiroom playback and/or voice commanding that Siri bloke.
I am right now sending a test playlist with different formats to that inherited Iphone to check what happens. Already installed three Hi-res players (Onkyo, Teac and Vox) on the device, but fear that's not the cleverest of ways to go ... ;-)
 

Playback:
What puzzles me a bit is the different SPL I have experienced, depending of source. I have fixed output on the DAC and fixed volume settings on my actives, and opted to let the WIIM control the output levels. I may try the fixed volume option of the WIIM to avoid these peaks.
I could control the bitrate via Bubble controller. That feature may come soon for the WiiM app too. Using the DLNA server provides record covers´.

Network:
In my setup, when serving AND controlling from the PC, I do get hiccups from the 192kHz files.
While using the PC/JRiver only as server to the controller (WiiM/Bubble) on my mobile phones and using the WiiM as endpoint to the Soncoz DAC  I can't reproduce this problems. Ergo, the problem isn't about the device under review but rather on the source and/or the intermittent device (the Ethernet/WiFi router).

Actually, with the test setup, my Win 10 Pro Music server and the NAS (both on Ethernet) are out of play, in order to avoid even more complications. Not used to hiccups at all playing music with my Ethernet bounded network, thus rarely using WiFi for streaming in my system. If I would do so more often, I guess I would want to try upgrading to the network quality needed.

For the standard usage with my mobile phones, the streaming inside the wireless network (between 73% and 85% quality) is seamless and smooth.
I would think it is a matter of personal philosophy/preference making a decision about the suiting streaming options.
I may imagine 4 WiiMs in the network for multiroom streaming, 16/44 content up sampled to 24/192 from an Ethernet bound office PC and attached external USB hard drive may be challenging. Would 24/96 or 16/44 do justice to the setup ?

As we love choices, we may need to sacrifice existing shortcomings (meaning: upgrading network quality) to achieve the highest goals, or reasonably accept that not everything is possible on an existing standard.