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.
Midi footswitch - The Crossflow Controller
Just came across this serious looking loop station midi controller. Custom made in the UK and on eBay uk for £599. It's got an audio interface built in. The maker says it's for use with a laptop, but there's an iPad mounted as a remote for the laptop looper plugin (mobius) and there's an iPad socket built in to the side of the unit, so I'm guessing it wouldn't take too much for it to be deployed as an iPad controller?
Anyway, hats off to him/her for the "I needed this, so I built it" philosophy and skills. If I had some money to burn I'd buy one, only I already burnt it (several times).
Here's the eBay link (more pics there):