What do you use for a monitor to program the KPA? Does it sound good from the monitor? I have had this issue through a PA and it was the a combination of the sound guy not setting up the board flat and some terrible cheap PA speakers. Now when it did happen it as usually on profiles with high gain settings, most of the others were fine. But this has only happened to me once and for the evening I tweaked the output EQ settings of the KPA to get it close and had the soundman adjust the board. If he is using cheap PA speakers I'm sure not only your guitar but the entire sound is bad. I have since used it from sound companies using JBL and Yamaha with high end mixer, never a problem with XLR out. In fact I have had the sound man come up after the set and ask what the hell are you playing through, the sound is amazing.
I would experiment with other possibilities, if you have access to another PA try that because if it sounds good out of your monitor then there is nothing wrong. What is your main output set on with the KPA? Try to keep it down and send a moderate signal to the board. Then make sure the sound man keeps the gain down and use the slider, if you need more volume then turn the gain up slightly until satisfied. Also check the XLR cable you are using make sure there is nothing wrong with it.
Live I either use my FRFR or main XLR out and use the house monitor mix to hear my guitar. Most of us do use the XLR out and either a FRFR or IEM's and others use a cabinet. Good luck and keep us posted. It's always nice to read the solutions in case we come across issues.