Dante
Try low heat like those heat guns. Sometimes I would expect that blue threadlocker might be used to ensure to be sure the knobs wont came loose. Failing that, drill the screw out slowly and use a very small easy-out. Due to the heat of the drill going round helps the easy-out to work better. You may sustain a little damage to the top of the thread but all you do is countersink the hole a little or run a tap /die through it. When you get a new screw for the knob if you are going to pull it apart regulary put some 'never seize' on the thread to make fror easier removal. Hope I havent stated the obvious so have fun.
