Your use case is surely a rather extreme one.I hope you have set the V3 Monos to 25 dB gain.
However, this point has actually been criticized from the beta stage on. WiiM didn't listen.
Ironically, third party apps like e.g. Tidal using Tidal Connect can set the volume in increments of 1%. At least some TVs can do it as well through HDMI CEC. It's just the WiiM Home App and the hardware remote that are limited to 3% steps.
I forgot to change them to 25db. That helped. Good catch.