When it comes to sharpening, I prefer to avoid Diamond Steel stones, and stick with waterstones and ceramics, as I've found that I get a better edge with them. I've owned a number of karambits and hawkbills, and I've found that the best way to sharpen them is to use coarse, rounded stones, and work your way down to round seramic stones. By doing that, you get a hell of an edge, especially if you keep the bevel between 25 and 30 degrees on each side.