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 Messenger - New free app
[from website] This plugin came to life as an answer to the lack of MIDI processors for iOS. One of us needed to send Bank/Program Change messages when a project was loaded in AUM, and the only solution for this task appeared to be writing hexadecimal codes in StreamByter. That didn't feel right. So here it is. By the way, it's also available for macOS as an Audio Unit.