I don't know enough about the head construction of the 425 Max head. If it's a solid head with no openings.
1.) Most good clubmakers would use hot melt to deaden sound but that would also add head weight. I typically use this method with my hot melt gun.
2.) Find some fiberfill yarn thicker than regular wool yarn. You can find it at fabric or craft stores. Pull shaft drill out plastic plug at bottom of hosel to access inside of head and stuff as much as you can get into head. Fiberfill yarn is quite light won't change head weight and will deaden sound the tighter you can get it in the head the more muted it will sound.
