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.
Remember the Korg Legacy Collection?!
Back in December 2017 is was rebadged as 'Korg Collection', with the following statement:
Some features widely requested by users will be added to the KORG Collection in future updates. We plan to [...] refine the user interface on a large-scale among other improvements but until then we hope you love all the new features so far and enjoy making music with the KORG Collection of synthesizers offered by KORG.
1 year 9 months later, nothing!