Go 4-1 and win a conference championship. Win a home playoff game against a 3-9 team and you're in the State quarterfinals.
I don't know where your classifications list is from but here's the current list:
Also, many 4A schools have larger student enrollment than some 5A and 6A schools. They should combine most of 6A, 5A, and 4A. Have a STATE tournament. They already play regular season games across the classifications.
Getting to the State Quarterfinals should really mean something and the State Championship would be less likely to rotate among the same half dozen high schools.