There are millions of solutions which could be used.
I have always wanted to fill the whole area between the top of the cabinets and the ceiling with light fiberglass batting (like the pink stuff) with a simple wood frame stained to match the cabinets with the open areas filled with black fabric to let sound through. It would look decent and be the most effective of the solutions.
Another is to get a bunch of foam sheets and just cover the entire wall areas with no gaps across all the area up there. It would look like a proper wall treatment and absorb a goodly amount of sound, softening the room a bit. You can get foam in damn near any color. I do recommend a fire retardant model of foam, though, which can cost more.
Yet another approach could be to just pile up sheets of compressed OC703 fiberglass on top of your cabinets as high as you can without it being visible from the below. This could be even if you also cover the walls with foam.
Finally, six words: massive amounts of fluffy stuffed animals.
My living room abuts the dining room and kitchen and I have slap echo issues too. I have considered addressing the acoustics up there because it is the primary viewing spot, but I just cant pull the trigger and I would still prefer that if I were going to treat a room the basement would be first.