I got the cheaper digger and it works great on most augers, but not with a kdrill. Haven’t figured out a way to use it.
They are apparently working on a larger adapter for the reason you are having issues. I contacted them after I purchased my mount because I have a quick connect coupler with extension on my strikemaster and the diameter of the coupler is too big to fit in the cradle.
They told me they are working on a design for the k drill. Perhaps email them and see if they are done yet and they will likely send you one.