To make the butter sauce, allow unsalted butter to soften to room temperature. Combine all other ingredients with butter and blend till smooth. Refrigerate until needed. To make the spice mix, combine all spice ingredients and mix well. Place in a spice shaker.
Preheat grill to 350-375 degrees. Melt 1/2 cup of unsalted butter and brush the belly side of each fillet evenly. Sprinkle spices on fish. Place fish on grill belly side down and repeat this step for the opposite side of fish. Grill each side approximately 3 to 4 minutes.
While fish is cooking, melt half of the refrigerated butter sauce from the first step in a saute pan. Add crawfish and crabmeat to saute pan and stir occasionally until hot. Set aside. When the fish is ready, reheat the butter sauce and add additional butter sauce from the first step to make the sauce creamy. Serve sauce immediately over the fillets.