Trim fat from steak. Combine soy sauce and next 4 ingredients in a large heavy-duty, zip-top plastic bag; seal bag, and shake well. Add steak to bag; seal bag, and shake until steak is well coated. Marinate steak in refrigerator 8 hours, turning bag occasionally.
Remove steak from marinade; discard marinade. Place greased grill rack on grill over medium-hot coals (350° to 400°). Place steak on rack; grill, covered, 6 minutes on each side or to desired degree of doneness. Remove steak from grill, and let stand 10 minutes; cut diagonally across grain into thin slices.
Combine butter and remaining ingredients in a small mixing bowl; beat at medium speed of an electric mixer until fluffy. Serve butter mixture with steak.