PPro CS6: How to adjust volume level in Source Monitor?

Hi,

I'm using Premiere Pro CS6 on Windows...

PPro plays back audio full volume in the Source Monitor, regardless of Windows system volume levels, Audio Mixer panel settings, etc.  Those controls all work fine in setting the volume level for the main sequence itself, though. 

Any ideas on how to simply turn down the Source Monitor volume so it's not blaringly loud?

Thanks,

Chris