Man some disinformation in this thread...
RSK is Rally Sport Kompressor
Kompressor is a German word(and contrary to popular belief, the word being used in this form by Subaru has nothing, absolutely nothing to do with Mercedes Benz), its meaning is literally compressor, or to compress something, or to increase its pressure (and contrary to popular belief does not mean Supercharger, that is just a literal translation).
The word Kompressor literally means Supercharger or Turbo charger.
Here is a link that may help some on the word Kompressor:
http://en.wikipedia.org/wiki/Supercharger