Omnipotence is provably impossible: "Could Jesus microwave a burrito so hot that he himself could not eat it?" etc.
Super-intelligence, not so much — there's plenty of examples of above-average humans in many areas, and no reason to think that putting the top expert in each field into one room is impossible, and no reason to think that this configuration cannot be implemented in software with a sufficiently powerful computer.
And that's without the things that machines already beat us at, because super-human chess playing software is easily available, and computers that do arithmetic better than the entire human species even if we were all trained to the level of the current world record holder are cheap enough to be given away free glued to the front of a magazine, so there's no single person who has a particular advantage with those things.
What chess does do, is give an example: if I was playing a game with Kasparov, I would have no idea which move he might make at any given moment, but despite that I'd still expect him to win.
With an AI, I don't even necessarily know what "game" it's playing even if I'm the one who wrote the utility function it's trying to maximise.