I'm 6'7" so I can sympathize with the problem you're having. The problem is that ALL of the new sport quads are being designed for the guys that race them who are generally of 'average' build: 5'5"-6'0" tall and 160-200#.
Just sit on any of them and you'll realize that. As larger people, we just have to learn how to adapt ourselves to the machine. Certainly, as was noted, some aspects of the machine can be adapted to accommodate us, but for the most part we are stuck with what is there.
Good Luck!
God must love stupid people; He made so many.