Toss potatoes with 2 tablespoons butter in a 2-quart microwavable dish. Microwave, covered, on HIGH 8 minutes or until potatoes are tender, stirring halfway through cooking.
Place potatoes, shrimp, sausage, corn and onion in large bowl. Toss with remaining butter and Crab Boil. Divide mixture evenly and arrange in center of each sheet of aluminum foil. Bring up sides of foil; double fold top and ends to tightly seal packet.
Grill over medium-high heat 10 minutes or until corn is tender and shrimp are cooked through. Sprinkle with parsley and additional Crab Boil, if desired. Garnish with lemon wedges before serving.