Are you saying you want to use the <node3D>.playsound command but also manipulate the sound volume yourself? If so, look at the following:
Code:
import viz
viz.go()
ball = viz.add('ball.wrl',pos = [0,1.8,2])
slider = viz.addSlider()
slider.setPosition(0.5,0.2)
slider.set(1)
sound = ball.playsound( 'boing!.wav', viz.LOOP )
def changeVolume(value):
sound.volume(value)
vizact.onslider(slider,changeVolume)