I recently purchased an Amplifi 150 with a shortboard controller, and after resolving a teething problem I am very happy with it. The range of tones is amazing, but you know this already. Anyway, I was initially disappointed not to have an on-board looper, but the USB socket came to the rescue. I connected my iPad via USB using an iPad camera adapter which comes with a USB socket. I had already been playing around with "Loopy", which is the best looper available for iPads and iPhones IMHO. Anyway, the short story is that no fancy setup is required. Loopy can immediately communicate in BOTH directions with an Amplifi after you plug in the cable. You can lay down a loop, then it will play back through your Amplifi while you lay down other tracks, and then you can sing & jam with your loops, switching sounds on the fly, with all the sounds of previous loops retained just as you want them. Loops can be of different lengths, so long as they are correct multiples of each other. All loops can be saved for later on your iPad.
This is by far the best option for looping with an Amplifi that I have found. I guess if you had a commercial looper with a footswitch that communicated via the USB then then that might be better, but for the minuscule cost of Loopy I'll put up with the need to place my finger on the screen to begin recording another track. Loopy gracefully allows you to foreshadow a recording track and it starts recording when the other loops come to the beginning.
Enjoy.