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.
midimittr 2.0 / open source
Since midimittr is (much to my surprise) still heavily used, I decided to give it a UI overhaul, a rewrite to Swift and subsequently open-source the app as well.
It's available on the store (https://itunes.apple.com/us/app/midimittr/id925495245?mt=8 - however Apple's desktop web view seems botched and produces an error right now) and on github at https://github.com/sieren/midimittr