According to the coach I worked with recruited athletes at USMMA get 2 benefits in the admissions process. First you get significant extra points on the subject portion of the scoring - leadership/athletics/ec, etc. I can't remember the exact # of points but it is bascially enough to points to put you at a max score for that one area which is approximately 30% of the overall equation.
Another benefit is that the coaches usually manage to get their people considered earlier in the process - November/December time frame. I am not sure if this makes a substantive difference but it is certainly nice to know early on if you are admitted.
If you are still a junior, track down the appropriate coach now. Be persistent because they are very busy and may not get back to you right away. Visit the school, work out with the team and ask the coach to better explain the process that I mentioned above. Good Luck.