Whisk together the sherry, cornstarch, and egg whites until the mixture is foamy. Add the beef and toss to coat the pieces well; set aside. Heat 4 tbsp. peanut oil in wok. Fry quickly, just until crispy and browned, remove to wok rack to drain. Add remaining 2 tbsp. peanut oil to wok. Add orange rind and red peppers to hot oil in wok. Stir-fry until orange rind begins to darken and aroma from oil becomes pleasant. Add remaining ingredients and stir until bubbly (add more beef stock if too thick). Add fried beef and toss to coat with sauce. Serve at once with steamed white rice.