Default volume of SATB

When playing the orchestral score in MS4, all the new MuseSounds sound really great. The only problem is that the default volumes of the SATB voices are so low that even when I raise the Mixer sliders to the very top, they are not loud enough. I have to raise the Master slider which makes all the other instruments TOO LOUD. Is there a way to reset the SATB voice default volumes so that I can create a proper balance between the voices and the instruments? I was unable to find a fix for this in the documentation.