PREHEAT grill to medium-hot heat. Cook onions and garlic in butter in large skillet on medium-high heat 10 minutes or until onions are tender. Add steak sauce and wine; mix well. Bring to boil.
PLACE steaks on grill. Grill 6 to 8 minutes on each side for medium rare (145°F) to medium doneness (160°F). Serve topped with steak sauce mixture.