Just a quick note. I've just read Inner Drumming by George Marsh. Marsh's book could be used by any level of drummer. The focus is on rhythm, but as understood and explained through the limbs; awareness of the body is the real point. To this end, the notation removes any notion of drum set, concentrating on the four limbs only. This openness allows the creative musician many ways in which to use the notation. Well worth a look.