Grease five 6" x 3" x 2" loafpans. Line bottoms of loafpans with wax paper; set aside.
Melt butter and chocolate in a heavy saucepan over low heat, stirring often. Stir in coffee granules. Remove mixture from heat, and let cool 15 minutes. Pour into a large bowl. Stir in brown sugar. Add egg yolks, stirring well. Add 2 tablespoons Kahlúa and vanilla; stir well.
Combine 1 1/2 cups flour, soda, and salt; add to chocolate mixture. Combine dates and next 3 ingredients; sprinkle with remaining 1/2 cup flour, tossing to coat. Stir fruit mixture into batter. Beat egg whites at high speed of an electric mixer until stiff peaks form; fold into batter.
Spoon batter evenly into prepared pans. Bake at 300° for 1 hour and 15 minutes or until a wooden pick inserted in center comes out clean. Let cool in pans on a wire rack 10 minutes; remove from pans, and brush loaves with remaining 1/4 cup Kahlúa. Let cool completely on a wire rack.
Wrap fruitcakes in Kahlúa-soaked cheesecloth. Store in an airtight container in a cool place at least 1 week before serving. Pour a small amount of Kahlúa over each loaf every week up to 1 month. To serve, slice with an electric knife.