Bring a large pot of lightly salted water to a boil and stir in macaroni from the packages, retaining cheese mix packets for later use. Cook macaroni at a rolling boil over medium heat, stirring occasionally, until tender but still slightly firm, 8 to 10 minutes. Drain and rinse macaroni with cold water. Return cooked macaroni to the pot. Mix butter, chicken broth, and tomatoes with macaroni and bring mixture to a simmer over medium heat; stir in garlic powder, cumin, dry mustard, pepper, and contents of cheese mix packets. Stir in milk and reduce heat to low; heat soup almost to a simmer. Do not boil. Serve soup in bowls and top each serving with about 2 tablespoons of sour cream.