The latest Grain Science update has added Audiobus support!
Grain Science is still my favorite way to play with granular synthesis on the iPad, because it isn't trying to be "experimental" or weird. It is just a solid synth that happens to do granular.
The ability to run this into some of the Audiobus enabled samplers opens up a world of possiblities.
What's new in 1.4:
Introducing Audiobus support — now you can stream live audio directly from Grain Science to other Audiobus-compatible apps!