Combine buttermilk and soda in small bowl; let stand for a few minutes. Beat egg whites until stiff in small bowl; set aside. Cream butter, shortening and sugar in large bowl until fluffy. Add egg yolks, one at a time, beating well after each addition. Add flour and buttermilk alternately, beating well after each addition. Stir in vanilla. Fold in egg whites. Stir in pecans and coconut gently. Pour into 3 9 inch layer pans. Bake at 350 degrees F for 25-30 minutes until cake tests done.
For Icing: Cream cream cheese and butter in bowl until well blended. Beat in vanilla and add confectioners' sugar gradually until of spreading consistency. Spread between layers and over top of cake.