I recently downloaded with minecraft launcher the new music but as I tried to listen the "boss.ogg" file with VLC player I noticed that it sounded as there was no music. So I opened it with Audacity editor and I saw that there was a music - but it was too quiet to be heard at all. Normalization with a sound editor fixes the problem.
So there is the boss music (and can be heard after editing it), but I don't think it's supposed to be that quiet.

Edited summary to clear the ambiguity.