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.
Comments
Focusrite, iconnectivity...
All class compliant interfaces (i.e. Any interface which dosn't need special drivers to connect with an ios device ) will do the job. The thing to consider next, is your budget & your requirements. IMO Focusrite offer great value. Lots of different options to suite most peoples needs. RME would be my other recommendation if your budget is higher........
https://www.gearank.com/guides/ipad-audio-interface#14109
This might help.
I use the Presonus iTwo and it works great.
Not sure if it has what u need but just got a novation audio hub.
Its Awesome!