PHILADELPHIA — On a rainy Thursday evening earlier this month, a horde of 30- and 40-somethings stream into the 3,500-seat Met Philadelphia concert venue, looking as if they’ve come from a smorgasbord of office jobs. The auditorium stage is tastefully stark, decorated only with a single table and a bouquet of pink wildflowers in a vase atop it. The room fizzes with anticipation.