Multiple medias volume control S4

[Karen DiMenna]

So while at the gym I enjoy listening to music AND being chased by zombies (Run Zombies! App) on my Samsung S4. I find it uberfrustrating that I cannot turn up the volume for Run Zombies so that I can hear the narration over the music playing in the background, simply because they are both media. The same applies with any use of multiple medias, like watching a movie and playing a game. Does anyone know is there a fix or an app out there for this?