There is a “vast underground world of amateur chamber music, whose members meet through friends, at parties and seminars, in community orchestras and on the Internet to share a common passion and a unique social network. Some have switched careers after a disappointing job hunt as pros, while others dust off old instruments as a hobby. But many plan on music as a satisfying avocation from the start — viewing their musical interests as a way to provide balance to demanding if often lucrative professions.”