They have change the unit…
You can’t engage the pad, because there’s no pad on UR22 ! 
UR824 have a pad for example.
With the older UR22 I have tried to plug guitars with direct boxes and always he same issue with the gain.
Even with a simple Audix D4 on a floortom, at the lower gain, the signal was clipping.
I hope you will find a solution.