To receive audio input to you iOS device and then output processed audio you will need an audio interface like the iRig or iRig Pre from IK Multimedia. These devices allow mono in and stereo out.

You will also need an app that does effects processing and can be controlled by the Motion Synth App via MIDI. A great example of such an app is Magellan Jnr. We used Magellan Jnr with the Motion Synth App to create this vocal effect: http://youtu.be/vOlIawT01uo?t=1m17s