I've had both in my home driving Avalon Acoustics Eidolons. These speakers are considered by some to be a difficult load but I still own a 60 watt tube amplifier that can drive them nicely.
The Kharma and the SE are both fine examples of class D design. In my system the Kharma had a more designed and refined presentation where the NuForce was more transparent balls to the wall. Both are musical to me. While their sonic differences are definitely a matter of taste I wouldn't consider one superior to the other.
As far as their ability to drive my speakers the Kharmas ran out of steam first but at a level I don't think anybody would realistically listen at. An often overlooked quality of class D amplifiers is their ability to play loud without fatigue. They both had more fatigue free gain than my, even more powerful, linear solid state amplifier.