While the meatballs are cooking, prepare the cajun sauce. In a large skillet, melt the butter over medium heat. Add the onion, and cook until slightly softened, about 6-7 minutes. Add the garlic, and cook for an additional minute. Add the flour, cajun seasoning, cayenne pepper, and a dash of salt and pepper. Stir to combine, and cook for about 2 minutes or until the spices are fragrant. Add the diced tomatoes, chicken broth, and milk. Stir to combine, and allow the sauce to simmer for 10 minutes or until slightly thickened. Stir in the cream cheese until melted, and then stir in the parmesan. Remove from heat. If the sauce is still not thick enough for your liking, continue to simmer and reduce.