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.
Considering updating to iOS 7? Wait!
We're on the cusp of iOS 7, and I'm here to urge caution: If you rely on music apps, please don't update yet.
iOS 7 audio is not ready. There are a wide variety of bugs that are causing performance problems, crashes and other problems in a large number of music apps.
This may change in the future, but until we see a few point releases for the OS, I strongly urge you to stick with iOS 6.