In large bowl, beat cake mix, water, oil, egg whites and coconut extract with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Pour into pan. Bake as directed on box for 13x9-inch pan. Cool 5 minutes. With long-tined fork, poke top of hot cake every 1/2 inch, wiping fork occasionally to reduce sticking. In medium bowl, mix milk, 3/4 cup of the whipping cream and the cream of coconut with whisk until blended. Microwave on High about 1 minute 30 seconds or until heated. Carefully pour mixture over top of warm cake. Cover; refrigerate 3 hours or until chilled.