Audiobus: Your virtual music studio.
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.
Sonar works True-Fi App
Just tried this with some Hesh2 Bluetooth cans. The app claims the provide a flat studio response on any headphones. Despite my initial scepticism must admit that the app makes a massive difference. Only problem being that the mobile version only works with Spotify unlimited and local music files. Currently free pre launch. Will eventually be on a subscription basis or £79 for lifetime licence. Suggest you give it a whirl