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.
iOS 15 Public beta 3
The public beta 2 was working pretty well aside from a few issues that I could work around. The public beta 3 breaks search in spotlight. I’ve gathered I can get it back with a full reinstall but haven’t tried that yet. Just a cautionary note to those considering upgrading.