I have the same problem.
I changed my hardware/speaker which basically led to change of default sound output device (the previous speakers were USB connected and separate sound device).
It seems the WoW clinet cannot find the default output device anymore. No sound at all in game. Sound.log shows the same error as Sayso above posted.
Tried deleting /WTF/config file, which did not change anything.
Any ideas or help, please?