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.
OT: Absolutely SUPERB composer tool
This desktop app is new, so you may not have heard about it. It's also relatively expensive, but the results I've been getting are phenomenal! After an hour I had a very pleasant string quartet piece that I can listen to again and again. It also does ambient, electronic, and several other genres. If you are stuck with writer's block, this could be the perfect tool. I've also used it as a source for noodling with synthesizer settings, because then I can focus on the synth instead of playing simultaneously. NOTE: I have no affiliation with this company or product. I'm just sharing what I think is a great but relatively unknown composition tool.