Preheat the oven to 350 degrees F. Lightly butter a 9- by 13- by 4-inch baking dish.
Bring a large pot of salted water to a boil over high heat and cook the macaroni until al dente, 8 to 10 minutes. Drain.
In a small bowl, combine the cream and milk.
In a large saucepan over medium heat, melt the 1/2 pound of butter and cook the onion and garlic until the onion is translucent, about 6 minutes, stirring occasionally. Add the flour, stirring constantly for 3 minutes. Add the cream mixture in a steady stream and whisk until smooth. Bring to a boil, stirring occasionally, 8 to 10 minutes.
Stir in 4 cups of the Cheddar, the American cheese, 1 cup of the grated Parmesan, the hot pepper sauce, and cumin. Stir until all the cheese has melted; the sauce will be very thick and creamy. Season with salt and pepper.
Remove the sauce from the heat and stir in the pasta. Pour the mixture into the prepared baking dish. Sprinkle with the remaining Cheddar, then the Parmesan, and finally the bread crumbs.
Bake uncovered on the middle shelf for about 20 minutes, until bubbling and brown on top.