Can you try running this in a command-line (replace /PATH/FILE by one of your files) :
gst-launch-0.10 filesrc location=/PATH/FILE ! decodebin ! audioconvert ! audioresample ! pulsesink
And see if it plays correctly, if not can you try with gst-launch-1.0 instead of gst-launch-0.10.
Also, in gmusicbrowser, did you try using mplayer instead of gstreamer (you need to have mplayer installed) ?
Can you try running this in a command-line (replace /PATH/FILE by one of your files) :
gst-launch-0.10 filesrc location=/PATH/FILE ! decodebin ! audioconvert ! audioresample ! pulsesink
And see if it plays correctly, if not can you try with gst-launch-1.0 instead of gst-launch-0.10.
Also, in gmusicbrowser, did you try using mplayer instead of gstreamer (you need to have mplayer installed) ?