This app was mentioned in 5 comments, with an average of 2.40 upvotes
/u/Banjo_banjo_banjo's note about the iPad is incorrect. There's an Android app, as well as PC, Mac, Linux, and for some reason Raspberry Pi software, if you don't want to use the iPad, or if touring engineers don't have one.
Edit: To add a note on the wifi thing, it's very hit-and-miss, as with everything wireless it completely depends on the venue and the environment.
Given that you're in a restaurant, you might have people with phones everywhere, and you have 20 different wifi networks in range because you're on a busy city block, for all any of us know. That'll significantly degrade your potential wifi performance. Also, your restaurant could be huge, and the XR12's wifi won't cover it.
Generally I'd suggest connecting everything you possibly can via ethernet, and beyond that using a professional-grade access point, but that's a worst-case scenario. For all I know the built-in wifi will work fine for you.
That would be great, thanks! The app is called X Air, here's a link: https://play.google.com/store/apps/details?id=com.behringer.android.control.app.xair&hl=en
More info: You can get to the mixing console by pressing "offline". Once you're there, you can move the volume faders up and down to adjust the decibel level of each channel (if you press the "fine" button, it's supposed to let you adjust them more accurately). On my phone, I have no problem adjusting the volume 0.1 decibels at a time, but on the Ellipsis, it just jumps all over the place and I can't get it to land where I want.