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 StoreAudiobus is the app that makes the rest of your setup better.
Anyone have any info on BandSim2?
Japanese with one YouTube demo...
http://nextsound.jimdo.com/
Just curious 
Comments
Looks like an update to band simulator. Which was not bad but a bit buggy. The instruments were all physically modelled but sounded pretty good. Didn't have AB IAA or anything like that though.
Composer in the chord BandSim 2 by NextSound
https://appsto.re/gb/dPK4ab.i
I own Band Simulator wich is now BandSim 1 (or BandSim), iphone app. As BiancaNeve says, it sounds pretty good. No AB, no IAA (and I don't expect them in the future). I like the way you can make rockin' sketches quickly. They have in the past another app called PowerBeat 2, wich works in a similar way.
I'll take the risk. At €2.99 it won't break my bank account.