Lightweight too!

I use my iPad primarily as a MIDI module for live use, with Audiobus, you can stack the hell out of things with Caustic.
My current favorite is Magellan > DFX > Caustic.
Magellan outputs 2 MIDI channels that Caustic sees. I can stack 2 sounds from Magellan, then 2 more in Caustic. Wall of sound!

Herman Muenster about Caustic