I’m using Volumio since some years, mainly for internet radio, with a hifi Berry DAC and it works fine, updated to latest version.
Now I tried airplay for audio via an ipad. It works, but the audio level seems to be quite low, even with highest output range on the ipad. So the amplifier has to be turnd up nearly to its limit. By returning to internetradio, I run into a very loud problem… 
Does anyone know about an option to adapt the levels of airplay and internet radio/Streaming?