App "Alarmy" is able to play iTunes song from background state... How?
They're using the audio background mode, it's listed in their info.plist.They use the "NoSound.mp3" file in their bundle to play silence, while in the background.They also have a "Sleep music" mode to get them through the AppStore.
For other ways that you can use, check out this article.
if ([[MPMusicPlayerController iPodMusicPlayer] playbackState] == MPMusicPlaybackStatePlaying){ NSLog(@"yes itune Player Sound is on");}else{ NSLog(@"NO itune Player Sound is not on");}