For rub, in a bowl stir together brown sugar, salt, mustard, five-spice powder, pepper, and garlic powder. Sprinkle over surface of ribs. Place on a tray; cover and refrigerate overnight.
For a charcoal grill, arrange lighted coals around a drip pan (with tongs, push coals to either side of grill, place pan between coals). Place ribs, bone side down, on grill rack over drip pan. Cover and grill 1-1/2 to 1-3/4 hours, brushing with sauce during the last 15 minutes of grilling (see instructions in Step 3). Add additional coals as necessary to maintain heat. (For a gas grill, preheat grill. Adjust for indirect cooking with flame on medium according to manufacturers directions. Place ribs on rack in a roasting pan, place on grill, and grill as above. After 1 hour carefully drain off liquid in pan and discard.)
Meanwhile, in a large saucepan stir together the remaining ingredients. Bring to boiling; reduce heat. Simmer, uncovered, about 50 minutes or until thickened, stirring occasionally (should have about 3 cups). Brush about two-thirds of the sauce over both sides of the ribs during last 15 minutes of grilling. Pass remaining sauce with ribs. Makes 6 to 8 servings.