Adding a volume control to a subscriber is not possible now as we normalized the audio and mix it with the system sound.
So your option is to latch onto the system audio.
One way I did that is as follows ( a hack for ios7) when I get a subscriber stream created callback

--
-(void) systemVolumeViewSetup

{

self.player = [[MPMoviePlayerController alloc] initWithContentURL:[self silentMovieURL]];

self.player.movieSourceType = MPMovieSourceTypeFile;

self.player.fullscreen = YES; // I think this may not be needed

self.player.shouldAutoplay = NO;



[self.player play]; // play to catch hold of system value handle



MPVolumeView *myVolumeView = [[MPVolumeView alloc] initWithFrame: CGRectMake(0, 300, 200, 150)];

[self.view addSubview: myVolumeView];


}