Whether the difficulties arise out of middle-aged boredom, serious illness or emotional troubles, Schnarch (Passionate Marriage), director of the Marriage & Family Health Center in Evergreen, Colo., offers a comprehensive guide for couples with intimacy problems. The book includes easily digested chapters on the basics of sex, how sexual relationships work, the use of drugs and surgery, psychological and emotional issues and orgasm. In a straightforward and comforting tone, Schnarch emphasizes the emotional aspect of sexual problems (even when there is an underlying physiological cause) and guides couples through the often difficult changes they have to make in their relationship in and out of bed. Using examples from among his own clients, he explores the way anxiety and tension in other aspects of a marriage can carry over into sexual relationships and gives advice about how couples can better approach each other. While much of his counsel isn't unique, Schnarch's positive, candid approach is appealing, and his tone is authoritative without being threatening. In fact, Schnarch says, "In the course of my life I've had every sexual dysfunction a man can have... I know about embarrassment, self-rejection, blaming myself or my partner, and withdrawing when I 'failed.' " There are no quick fixes or promises of overnight transformation, but those who want to make substantive changes in their relationship should first reach for this book. (Sept.)