You need to add the sound object in the main thread. Once it is added you should be able to play it in other director threads.
If it is necessary for you to add the sound object in the director thread, then you can install the pywin32 library for python and use the following code:
Code:
import viz
import pythoncom
viz.go()
def playSound():
pythoncom.CoInitialize() #Initialize COM
sound = viz.addAudio("quack.wav")
sound.play()
pythoncom.CoUninitialize() #Uninitialize COM
return
viz.director(playSound)