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.
How to use KQ Voice Plugins to enable GarageBand and AUM to exchange MIDI and Audio
Here's a new video in my series "Let's Play with iOS Music Apps." This one shows how I use KQ Voice Plugins to send multiple audio and MIDI tracks from GarageBand to AUM and even a way to synchronize the playback, so that the AUM transport starts when you hit play in GarageBand. It's a great way to play around in realtime with GarageBand and AUM and do things like use the MIDI based live loops to play instruments in AUM, take an existing GarageBand project and get some of the MIDI and audio tracks into AUM, or even combine the two to play together.
I haven't tried using the plugins to route audio or MIDI between other apps such as GarageBand and Cubasis, or Nanostudio, or BeatMaker 3, but it may work there too. A lot of new ways of using GarageBand in new and interesting ways are possible using the app. There's a lot of sharp talented people here in this forum, so it would be great fun to find out what else it can do.
I'm a big fan of the developer, Ryouta Kira, who also makes KQ Sampei - one of my favorite MIDI player and instrument apps, and he has been very active in updating the app and making improvements since it was released. I haven't had any crashes or issues with it so far either.
KQ Voice Plugins App Store link (US):
Let's Play iOS Music Apps: KQ Voice Plugins