On the one hand, why would you want to throw away something like neck reining, if he does it well? It is considered a higher level of training than direct reining. That being said, I ,too , prefer to direct rein and what Smrobs is describing, with the stiff as a board thingy, is something I see in a lot of neck reined horses. I guess that's why I don't like it so much. You get that feeling of a horse that turns like a boat, or a swinging gate, and if they are on their forehand, the centrifugal force is high. I prefer the horse so have enough awareness of the directional rein that he give that side of his jaw and bend lightly in the direction of movemen, "following" the rein.
I know that a well trained reiner is very light, bent to the turn and balanced. I just haven't had the priviledge of riding one.
I might spend some time on the ground with a halter, or with the bridle in hand teaching him to give to pressure on each side of the bit. YOu have to start small, rewarding the slightest give. Maybe he is resentful because you are trying to PULL his head around , rather than teaching him to GIVE around to the pressure on the bit.