Totally feel your pain, and have said many times that it worked fine (the peq graphics) before so it should be reasonable that they can make it work now.
If the was in the position to switch to a different mixer like the X32, I would look at the net cost. Since I already have the DL and iPads are pretty easy to sell on eBay and Craigslist I would look at switching to a iPad air. The net cost would be about $300.00. And I end up with the system I want, fully functional..
If I bought into the X32 (which I really like the fx and nice app), the investment with cable adapters would be about $500.00 if you sold the DL for maybe 400.00. At least you already have some behringer items so integration of the two would be pretty seamless for you.
While I would hate to spend anything to fix the system, sometimes it's just a necessary evil.