You guys should try out Music Locker, was my favourite when I was using Windows Phone. Supports FLAC, supports streaming from OneDrive, nice UI and the most important for me, it supports playlist-formats, so I can use all my playlists I use on desktop.
I've tried it out, but somehow during the scanning part the app gives an error or something like "Memory finished". I'm using it on a Lumia 830 running W10M though. Did you use it on WP8.1 or what?
Also, since you said "when I was using Windows Phone", do you mean you've left WP? T~T