Preheat the oven to 350°F. Spray a 13x9-inch baking dish with cooking spray. Set aside.
Macaroni: Cook the macaroni in a pot of salted water per the package directions until al dente. Drain well and set aside.
Meanwhile, pick over the crab meat removing any shells and cartilage. Set aside.
Sauce: In a medium-size heavy bottomed saucepan melt 1/2 cup butter over medium heat. To the melted butter add the flour, 1 1/2 tsp seafood seasoning, garlic salt, ground mustard and black pepper. Mix until the flour has been absorbed by the butter stirring constantly.
Gradually add the milk while whisking constantly to prevent clumping.
Bring the milk to a boil then immediately lower the heat to low. Simmer for 3-5 minutes gently bubbling stirring periodically to prevent sticking.
Turn off the heat leaving the saucepan on burner. Add the cream cheese to the sauce. Stir until melted then add 3 cups of shredded Cheddar and Monterey Jack cheese. Remove from the heat, stirring until completely melted.
Add the cooked, drained pasta and the crab meat to a large mixing bowl. (If you use a large pot, it can double as the mixing bowl.)
Pour the cheese sauce over the macaroni and mix until fully coated and the crab meat is evenly distributed.
Pour 1/2 of the macaroni mixture into the baking dish. Top with 1 cup shredded cheese. Repeat with macaroni then top with the final 1 cup of shredded cheese.
Breadcrumb Topping: Melt 2 Tbsp butter in a small microwave safe bowl. Mix with the panko bread crumbs, Parmesan cheese, and 1/4 tsp seafood seasoning. (Add more or less to your taste) Sprinkle on top.
Place into the oven and bake for 30-40 minutes or until the top has a golden color and it's bubbly around the edges.
Garnish with fresh parsley just before serving.