some time ago i wrote a shoutcast client, if nothing has changed since then, this are the steps to play make your app play audio while in background mode.
1. Add the audio background-mode to Info.plist:
Required background modes: "App plays audio or streams audio/video using AirPlay"
2. Tell iOS that your App wants to play autio while it is in background mode:
// Register for Background-Audio-Playback
[[AVAudioSession sharedInstance] setDelegate:self];
[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];
3. If your App starts playing Audio inform iOS about it:
[[AVAudioSession sharedInstance] setActive:YES error:nil];