Preheat oven to 450 F. Cook macaroni until it is almost tender. Drain and rinse thorougly with cold water. Melt butter in a 3-quart saucepan over medium-low heat. Slowly add flour, stiring constantly, to make a roux. When roux begins to darken in color slowly add the milk and keep stiring even though it may feel as if your arm will fall off at any minute. Add cream cheese and salt stirring until the sauce has a smooth and creamy texture. Fold macaroni into the sauce. Place 1/3 of the macaroni and sauce mixture into a buttered 8 x 8 inch pan. Top with a layer of cheddar cheese slices. Scoop another 1/3 of the macaroni mixture into the pan. Top with baby Swiss slices. Add the remaining macaroni mixture to the pan and top with the last of the cheddar slices. Bake at 450 for 15 minutes or until top begins to brown.