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.
Reclaimed 5GB of space by restoring iOS
I recently backed up my 32 GB iPad 3, reset to factory settings and then restored from backup. As a side effect, I went from 3 GB free space to 8GB free space.
Technically the backup should have restored everything that was on there, so not sure where the 5GB phantom space came from, but it might be worth a try if you've had your device for a while and are feeling space constrained.