if you were looking for a simple way to play multiple tracks and have complete control over their levels, panning, and even playback speed then this is the app for you. released for both the iPhone and iPad, the latter adds the ability to shift those tracks via 2-dimensional space with touch-and-draggable objects that correspond to each song-element in your queue.
this has the potential to become a platform for us for future development so do be sure to provide constructive feedback on the interface and basic functionality currently implemented. Thanks!
iPad: Sound On Sound
iPhone: Sound On Sound (μMix edition)