Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
GarageBand MIDI from MPE & Rozeta apps.
GarageBand is another app that only listens for MIDI but you can use apps like Midiflow or MidiFire to create connections that allow it to work. Once you’ve setup your connection you can host Rozeta in an AU host like AUM and route its output to that connection. You could route the virtual MIDI out port from any number of apps to GarageBand using this approach.
Here’s setups for Midiflow and MidiFire with AUM, you can do similar setups in Audiobus 3 too using Midiflow.
Here’s a video from the developer of GeoShred showing how to setup GarageBand control: