I use the Lansky 5 Stone sharpening system. I only use it on khukuris if it is very dull. I carefully use the stones by hand, without the frame, in tiny circular polishing motions to the tip of the edge like you would sharpen an axe. If the khuk is not very dull I just use a chakma either in the same circular polishing motions or like a kitchen sharpening steel. Never underestimate the chakma. They have a little bit of magic in them too.
Also search the HI forum for "Sharpening" and you will find tons of info.