In a large measuring cup, whisk together marinade ingredients until combined. Pour half of the marinade into a 9 x 13-inch pan, add steaks, and pour the remaining marinade over the steaks. Cover tightly with plastic wrap and refrigerate for at least 4 hours or overnight.
GRILL STEAKS:
15 minutes before grilling, preheat the grill to high. Remove tri-tip steaks from marinade and reserve marinade.
Place steaks in the middle of hot grill and cook 6-7 minutes per side. Remove steaks once they have reached desired doneness, and tent steaks with foil.
MAKE MARSALA MUSHROOMS:
While the steaks rest, make Marsala mushrooms. Melt butter in a large skillet over medium-high heat. When butter is melted, add mushrooms and cook, often stirring, until mushrooms release most of their liquid, about 5 minutes.
Add reserved marinade to pan and bring to a low boil. Reduce heat to low and simmer until sauce has thickened, about 5-8 more minutes.
TO FINISH:
Slice steak against the grain, smother with marsala mushrooms, and serve.