I am late to this thread, but this topic is really important IMHO.
The reason I say this is that I have been using lately my wiim pro plus as here described (connected directly to a power amp) The sound is great and I have been enjoying it so far.
However, I use Apple Music through Airplay on my Iphone. For this reason, I usually just use the Apple Music app. It has happened a couple times that, when the Iphone connected with the Pro Plus, the volume setting messed up somehow for some seconds and went full blast. Absolutely horrrible.
So I guess my question would be how to avoid this, the options that come to mind are:
a) Remain within the Wiim app (avoid using Apple Music and change to some other stremaing service)
b) Use (like proposed in this thread) an analog device like the Schiit Sys as a safety step in the signal chain. Turn its volume knob to almost max and then control volume from the Wiim App. However I wonder if this may introduce noise, distortion or channel imbalance issues.
c) Get a proper preamplifier and connect the Pro Plus either via rca or coax. However, this seems to be an expensive option.
Any thoughts or recommendations on this?