Confirmed sound works just fine on 5.5.0xp1 - in Editor.log I get:
AudioManager: Using PulseAudio: Default Output Device
On 5.6.0b3, no sound whatsoever - in Editor.log the following line appears:
AudioManager: Using Unknown: NoSound Driver
I straced the binary and I can see a lot of pulseaudio-related activity, so it would not appear to be a missing dependency, and the fact 5.50xp1 works on the exact same configuration would seem to indicate this is a bug.
I’m in the same boat. No sound in the editor (both when playing the game and when playing audio assets by themselves) but all sounds work fine when playing a game build.
Unity 5.6.0xb3 Linux
Ubuntu 16.04 LTS 64-bit
Intel® Core™ i3-4330 CPU @ 3.50GHz × 4
GeForce GTX 750 Ti/PCIe/SSE2
I’m pretty sure it’s not possible. You have to wait for the new build which hopefully has solved the illegal instruction problem. If you really have to work on sound at this moment, I guess you could downgrade to a lower version and upgrade later on.