Things look to work much better now.
First, I desactivated other audio plugins, especially soaudible (cloud audio), which seems to bring incompatibilities.
Second, I re-uploaded a bunch of sounds (the previously uploaded ones still didn`t work).
Et voila ! The single sounds are playing fine ;)
Still, the gallery is not playing, and the file names do not always stick and do not accept japanese encoding, but that`s a detail.
Thanks to all for reading this post,