Hi. I’m a complete newbie when it comes to troubleshooting Volumio, so please bear with me!
I’m running Volumio 1.55 on a pi, with a WD Cloud Mirror NAS, and BubbleUPNP on my android phone as a controller. I’m perfectly able to play uncompressed FLAC files via Bubble, but whenever I select a WAV or AIFF, it refuses to play, but giving no error message.
When I select these WAV/AIFF files using the Volumio web interface, they seem to play fine, and I can even see them in the Now Playing screen of Bubble. I can also push stop and play via Bubble, and that works too. However, when I look at the metadata of the file via bubble under Stream1 it says ‘MP3, 44100 Hz’ so I’m wondering whether this is actually playing the WAV in its full quality rather than transcoding it MP3.
I can also play WAV files from iTunes via AirPlay, but I appreciate that perhaps the AirPlay protocol sends the WAV to the pi in a different way.
Browsing these forums, I’ve seen a few posts that seem to be related to the problem, so apologies for reposting what might be the same issue:
hangs-when-playing-wav-over-upnp-t2301.html
problem-playing-audio-l16-streams-via-upnp-dlna-t1423.html
They seem to cite a problem with MPD, and offer a few fixes which seem quite complex for me. But as these are fairly old posts, I just wanted to check what the latest advice might be, and if someone can have the patience to explain it to an idiot like me! 
Thanks very much in advance
Joel