Preheat oven to 350 degrees F. Meanwhile, melt 4 tablespoons of the butter in a non-reactive saucepan. When bubbly whisk in flour and cook for a couple of minutes, stirring every now and then. Slowly whisk in the milk and bring to a boil. Reduce heat to low and simmer, whisking on occasion for 3 to 4 minutes. Remove pan from heat and whisk in grated cheese. Stir vigorously just until cheese has melted. Then whisk in heavy cream to adjust the texture and season to taste with salt and cayenne pepper. In a mixing bowl combine sauce with sun dried tomatoes and drained macaroni and adjust seasoning. Transfer mixture to a 13 x 9-inch baking pan and spread it out evenly. Sprinkle bread crumbs on top and dot with remaining 4 tablespoons of butter. Bake until hot and bubbly, about 30 minutes. Let stand 5 minutes before serving.