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.
Possible Novation AudioHub 2x4 Tip for iPad & IDAM
This may be a non-tip, but thought I'd share in case you hadn't discovered it like me until this weekend...
If you have the AudioHub 2x4 hosted on the Mac, and the iPad plugged into one of the USB ports on the AudioHub, and enable IDAM, the AudioHub will pass audio directly to the Outs. I was under the assumption the USB ports on the AudioHub wouldn't pass Audio thru like this, so it was a nice surprise.