Heat and stir first 4 ingredients in large heavy saucepan on medium high until boiling. Immediately remove from heat.
Add cereal. Stir until coated. Place sheet of waxed paper on damp work surface so paper will stay in place. Turn out cereal mixture onto waxed paper. Press into 10 x 15 inch rectangle. Let stand for 15 to 20 minutes until set, but still warm.
FILLING: Beat all 5 ingredients on low in large bowl until combined. Beat on medium until smooth, adding more water if necessary until spreading consistency. Spread evenly over cereal mixture. Roll up, jelly roll style, from long side, using waxed paper as guide. Wrap in plastic wrap. Chill. Cuts into 24 slices.