When you check this option your audio should continue when you navigate out of the app. Are you saying that your audio still pauses when you navigate out from the app?
So, I had my game exported to Xcode and build to my iphone, when I am playing the game and I receive a phone call, then when I go to back to the game, the game has no sound at all, or if I close my game for around 10 seconds then go back to the game, game has no sound too, so everytime the game got suspended or interrupted, the game will have no sound.