I don’t know exactly what the writers intended, but from what I can gather from "Kung Fu Panda" I think I have figured out the secret of the Wuxi finger hold.
There is no secret.
The Wuxi finger hold is a bluff. The golden explosion at the end represents the last shreds of Tai Lung’s ego going skadoosh. Tai Lung had bound up all his self-expectations in obtaining the scroll, and when he finally looks upon it reflecting his own face, he says, "It’s nothing."
Po’s realization that there is no secret ingredient opens up numerous truths, among them that the Wuxi finger hold is a bluff designed to crush an opponent’s ego by using his fear against him. The secret of the finger hold lies in belief of its power. Once Tai Lung realized he had been fooled and had quivered in fear in front of Po, his mojo went bye-bye. Tai Lung was no more the big scary bad guy.
Tai Lung believed that the scroll held everything. He believed he was nothing. By this logic the Wuxi finger held nearly infinite power over him.
I figure Tai Lung didn’t die at the end of the movie though, the golden explosion simply a metaphor for his exploding ego. Tai Lung realized for the first time that day he was lost. Crushed and broken, without a sense of self, he is found limp and listless by the noodle duck. "Why are you lying there, snow leopard?"
"I am not the dragon warrior. I was defeated by a Panda. I am nothing."
The duck replies, "Oh, come now, I need help in the noodle shop. You would make a fine noodle chef. Come with me."
Tai Lung eventually learns humility, and by serving others he begins to realize his true power.
A noodle cook becomes the dragon warrior, the presumed dragon warrior becomes a noodle cook.