Combine soy, oil, sugar, Worcestershire, garlic, chives, and pepper in medium bowl. Remove 1/4 cup marinade and combine with vinegar in small bowl; set aside.
Place remaining marinade and steaks in gallon-size zipper-lock bag; press out as much air as possible and seal bag. Refrigerate 1 hour, flipping bag after 30 minutes to ensure that steaks marinate evenly.
Remove steaks from marinade, letting any excess marinade drip back into bag. Discard bag and marinade. Grill steaks as desired.
Transfer steaks to shallow pan and pour reserved marinade over top. Tent loosely with foil and let rest 10 minutes, turning meat halfway through. Slice steak or serve whole, passing reserved marinade if desired.