WHEN INSOUND , the Amazon.com of indie rock, was having a difficult time reaching its target audience in 1999, co-founder Matt Wishnow dreamed up a new way to get heard. With his team's help, Wishnow, 31, who started the New York City music seller in 1998 with Ari Sass, 32, periodically chooses promising, actively touring independent rock bands and requests at least four free, unreleased tracks to put on a limited-edition CD. Insound then presses 1,000 copies of the exclusive tracks, giving 500 copies to the bands to sell during their tours.The bands keep the money they earn as an incentive to participate, and Insound gets exclusive merchandise to sell," explains Wishnow. Even better, branded Insound goods get into the hands of the company's key audience--people who love indie-rock bands. This promotion is hitting all the right notes: It has delivered at least 20,000 new customers to the $4 million company in less than three years.