Heat oven to 350°F. Greas and flour 13x9-inch pan. In large bowl, combine cake mix, brown sugar and peanut butter at low speed until crumbly. Reserve 1/2 cup peanut butter mixture; set aside. To remaining peanut butter mixture, add water, oil and eggs; blend at low speed until moistened. Beat 2 minutes at high speed. Stir 1/4 cup of the chocolate chips and 1/4 cup of the peanut butter chips into batter. Pour batter into greased and floured pan.
In small bowl, combine reserved 1/2 cup peanut butter mixture, remaining chocolate chips and peanuts; sprinkle evenly over batter.
Bake at 350°F. for 40 to 50 minutes or until toothpick inserted in center comes out clean. Immediately sprinkle with remaining peanut butter chips; gently press into top of cake. Cool completely.
Tip: Semi-sweet chocolate chips can be substituted for the peanut butter chips.