Liberally sprinkle the steaks on both sides with salt and pepper. Grill the steaks until just slightly less cooked than desired. Set in a foil pan, top each steak with 2 tablespoons sliced butter and cover with aluminum foil to rest about 20 minutes.
Remove the steaks to a cutting board, reserving the juices in the pan. Chop the steaks into 1/2-inch cubes, then return them to the pan with the drippings, cover and refrigerate, at least 4 hours and up to 3 days.
At game time: Preheat a grill for cooking at about 300 degrees F.
Drizzle steak sauce over the steak to taste, then cover the pan again and place the entire pan on the grill to reheat, about 10 minutes. Stir the steak and continue to reheat until warmed through.
Crack the eggs into a large bowl and whisk together with the milk. Place a nonstick pan on the grill and melt the remaining 4 tablespoons butter in the pan. Add the eggs and cook, stirring frequently, until scrambled and cooked through. Meanwhile, wrap the tortillas in foil and warm them on the grill.
Build the tacos and serve immediately, topping with hot sauce to taste.