Hi Ash
I use the ditto mini so I only have one output, I use a 1/4 inch mono splitter cable other wise the looper only plays out of one channel/speaker.
I just had a quick look at the Ditto x4 manual, it looks like you would just connect the mono to the KPA alternative in and the stereo to the KPA return. I don't think the stereo out put on the Ditto uses a TRS, I think you need to use both to get stereo, The mono connector sends both L/R if the stereo connector is not used. so for stereo they are basically a left and right output (maybe someone else with a Ditto x4 can confirm).
If however I'm wrong you can get a 1/4 inch stereo (TRS) splitter which would work fine. Just use the alternative in and the return inputs on the KPA.
It should be quite easy to test by connecting each of the outputs to your Kemper.
P.