Unconventional,
I have given this topic a great deal of thought and want to share with you what I think.
First let me say that I agree with you that the current high school system is not set-up very well for athletes like yourself who are trying to move from the state level to the national level competition and eventually develop into professional level runners. High School tracka nd cross country often require weekly and even twice a week racing which is not how runners at your level develop the best. Additionally many high school coaches (but certainly not all of them) do not have the expertise to help a runner make the jump from the state to the national level.
But now let me say that this doesn't mean that you can't make the high school system work. There are definate advantages to the high school system as well, including organized and well recognized local, regional and in some cases national championships, the opportunity top race against your peers and opportunity to help and support your team and school (which helps in social peer groups as well).
Here are some steps you can take to make the system work for you.
1) Secure good coaching, capable of taking you to the next level. It looks like you feel you have done this. Now get the cross country and track coach at your school to by off on letting this guy coach you during the school season as well. Be diplomatic and be sure you stay a memeber of the team as much as possible. Enlist your outside coach to help by asking him to call your school coach if needed. Remain calm and well reasoned and make sure not to get emotional or confrontational but let him know you want to be part of the school team but want to progress to the next level as well. Make the school coach feel as much a part of your running as you can while still taking your direction from your outside coach (diplomacy)
2) Once the coaching question is agreed upon, its time to talk about racing schedule. Take this one season at a time. Make sure you school coach knows that its pretty common that top runners such as yourself don't race every week and in every meet your team runs in. Pick out 1-3 bigger invitationals during the XC season plus, conference, regionals, state and Foot Locker/Nike. Hopefully a couple of these you can win as a tempo run and won't have to race. Make sure your school coach knows you are looking forward to bringing the school another state title and maybe a national top finish.
Now if your schhol balks at this and refuses to allow any room for either or both of these you always have the option of not running that season for the school. there is no obligation to compete in a school sport. But don't close the door on the next season or future options. Again keep it unemotional and make sure everyone involved knows you are just trying to do what is best for your long term development. Avoid taking and small prize money in local road races or free shoes, etc from any running stores, as they jeapordize some future options you may be interested in down the road. You can still compete in things like Foot Locker or Nike XC and can probably get into a few invitaionals (either HS or Collegiate) by contacting the meet directors or having your outside coach contact them.
In short, try and make it work but if it can't work out then make sure you don;t jeapordize your future options for small dollar items.
Good luck and fast running.