Audio Dropouts when Off Screen

Whenever I am using both Mainstage and Ableton for a live show, I will get audio dropouts, buzzing, and occassional system crashes if the Mainstage window isn't in view. The only way I've been able to fix this is by having Ableton on one desktop and Mainstage on another. I have to start the track on ableton then switch desktops back to Mainstage before I start playing keys. This seems to happen with any computer that we use. So far we've tried a 2011 MacBook Pro, my personal 2011 MacBook Air, and we've tried a 2015 Retina pro. All are running Yosemite. Has anyone had issues with this before or found a fix?