I'm using an iPad app called Loopy that communicates with my Amplifi 150 in both directions using the the USB. You need the camera adapter for your iPad, which comes with a USB socket. No fuss, no setups, just plug and play. Loopy records from the Amplifi and then plays back to the Amplifi through the USB cable. It's great. The only improvement you'd have with a built in looper would be the ability to control the looper with the shortboard, but Loopy is easy to run with a simple finger touch. Loops can be saved and played back later.
Enjoy.