Combine soy sauce, garlic, brown sugar, lemon juice, oil, onion and pepper. Pour over the steak, cover and refrigerate for 6 hours or (ideally) until the next day.
Lift steaks from the marinade and drain briefly, save marinade and boil it for 10 minutes in a small saucepan. Place the rib-eyes on a barbecue and grill for 6-8 minutes for medium rare, turning once and basting with reserved marinade.
Serve the buffalo rib-eye steaks with barbecued beans, barbecued corn on the cob, and Indian fry bread.