This is an example implementation of using AVAudioUnitSampler with AVAudioEngine and Apple's built-in effects. The Controls and Keyboard are from AudioKit and the MIDI comes from MIDIKit. It doesn't use any third party libraries for the audio engine. Work in Progress. :D

(Click the image to watch How to Make an Instrument App with AVAudioUnitSampler for iOS + AudioKit & MIDIKit)