So, this is really clever! fostervf16 over at YouTube is using the PreSonus 1818VSL USB interface with his iPad running WaveMachine Labs Auria. He’s found a way to connect the 1818VSL to his iPad using a data card reader, of all things. iPad > Card Reader > 1818VSL. All of this stuff is running off the iPad’s battery.
At the time of writing, I don’t have any insights about what this will do to your iPad’s battery charge. Should you have the necessary components, give this a shot… but save often.