Enabling the gapless option (-gapless-audio) in SMplayer2 doesn't work. So probably it (the same command) won't work in Gmusicbrowser as well.
I've tried all of the Linux music players, but only those consistently support gapless playback:
Adding the Gstreamer developer PPA solves the gapless issue in Guayadeque and may do so in Gmusicbrowser as well. Guayadeque got better by the way, and it's better than GMB.
You can find the Gstreamer developer PPA here.
Enter in a terminal:
sudo add-apt-repository ppa:gstreamer-developers/ppa
sudo apt-get update
Then launch Synaptic and on the left click Status, then click Installed (upgradable) and upgrade all the gstreamer related packages. I've left one of them asking to remove many other packages. Installed others and closed Synaptic.
Then Update manager itself asked to upgrade the one I've left un-upgraded before. Updated this as well accepting the remove gnome-media warning.
No problem so far. Guayadeque plays gaplessly now.