Ahh I see now, thanks for finding the context.
a runner-up - a person/thing/organisation that comes second in a competition. A distant runner-up would be one who was a lot worse than the winner. Imagine a race - the person coming second does so half an hour after the winner. They are a distant runner-up. (see the winner crossing the line and who is that in the distance?)
He is saying that even those famous composers, if they formed a band, would not be as good as Tenacious D ![Big Smile [:D]](/emoticons/emotion-2.gif)