1.
In a medium mixing bowl, combine the soy sauce, oil, Worcestershire sauce, brown sugar, garlic, chives and pepper.
2.
Remove 1/4 cup of the marinade and combine with the balsamic vinegar. (This will be used as a finishing sauce). Set aside. Place the remaining marinade and the steaks in a gallon-size zip-lock bag. Press out as much air as possible and seal the bag. Refrigerate at least 1 hour (not over 4 hours), flipping the bag after 30 minutes to ensure the steaks marinate evenly.
3.
After marinating, remove the bag with the steaks from the refrigerator about half an hour prior to grilling. Prepare your grill for high direct heat.
4.
Using tongs, remove the steaks from the bag, allowing excess marinade to drip off. Discard the marinade. Lay each steak on the grill (the fire will flare up a little as you do, but hang in there!). Allow the steaks to grill for 2 minutes without moving them around. Rotate each steak 45-90°, place it on a hot portion of the grill and let it cook another 2 minutes. (This gives you those professional-looking cross hatch grill marks!). Now with 4 minutes grilling time on the first side, use your tongs to flip the steaks (again onto a hot portion of the grill) and let them cook 2 minutes. Rotate them 45-90° again and cook them 2 more minutes.
5.
Place the grilled steaks in a shallow baking dish and pour the finishing sauce over them. Cover loosely with aluminum foil and allow them to rest for 10 minutes before serving