Stop reading this and buy this – AUM - Audio Mixer Review

This is probably the best thing to come out since audiobus, while you're at it, pick that up too. It links everything you have in a convenient, intuitive package. Audio units, inter app audio, midi even audiobus, hell you can route it back to itself with audiobus. The interface is clean and elegant, it makes you feel like this it what iOS music making should've been since its inception. In short, if its on sale, buy it NOW, if its full price, buy it anyway! Just buy it if you've ever been serious about iOS music making.
Review by Rayato on AUM - Audio Mixer.