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.
Mac AU vs iOS AU
Forgive my ignorance as my only real Apple knowledge is the iPad, but what is the difference between Mac AU and iOS AU? In my short search, it seems that they should be compatible with each other which would imply that they could run across systems. That then makes me wonder why there aren't more AUs on iOS from the Mac versions?