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 StoreAudiobus is the app that makes the rest of your setup better.
PSA: Tascam iUR2 SDOTD
This thing could be cool or a total POS as I've never seen it before. But a 2in/6out audio/midi interface for $40 deserves a look at least.
http://www.musiciansfriend.com/stupid/?icid=204625&noPopup=true
Be sure to read this before you jump. But I bet this disclaimer only applies to the 30 pin dock connection and if you hooked it up via USB/CCK it would work like any other core audio/core midi device but not sure.