Combine first 8 ingredients in a large mixing bowl; beat at low speed with an electric mixer until crumbly. Press into an ungreased 13" x 9" pan. Bake at 350° for 12 to 15 minutes or until lightly browned. Sprinkle with marshmallows; bake 1 to 2 more minutes or until marshmallows begin to puff. Cool in pan on a wire rack.
Combine peanut butter morsels and next 3 ingredients in a large saucepan; cook over low heat until smooth, stirring constantly. Remove from heat; stir in cereal and peanuts. Spread cereal mixture over marshmallows. Cool completely in pan on wire rack. Cut into bars.