Audio Generator

I need an audio generator black box for an iPad app we are developing. I want a simple set of arguments I can pass into your method and through a set of of controls you have also given me, play the audio through the iPad speaker. A piano app would make a good model and starting point. This must be polyphonic. Here is what I would need to pass you: Any number of tracks/channels; A series of MIDI notes and their durations (you specify the durational units); Pan, volume, General MIDI instrument sound; Mixer w/Graphical interface; Ability to use Apple AU units such as Apple reverb, EQ, etc. Master tempo, volume, speed (tempo). Actions: The usual suspects - Play/Pause/Rewind/Fast Forward, etc.