1. New York Festival of Song Merkin Concert Hall, 129 W. 67th St., nr. Broadway; 212-501-3330 The evening’s program, “All Together Now,” showcases music written expressly for group performance, from Monteverdi to the Beach Boys.2. St. Luke’s Chamber Ensemble Zankel Hall, Seventh Ave. at 57th St.; 212-247-7800Mozart’s Eine Kleine Nachtmusik is the centerpiece of a romantic program that also includes Schoenberg’s Transfigured Night, and Debussy and Chopin. 3. Royal Concertgebouw OrchestraCarnegie Hall, Seventh Ave. at 57th St.; 212-247-7800The excellent ensemble is in from Amsterdam; on the 14th, it will play Shostakovich’s heartfelt Seventh Symphony (“Leningrad”). 4. “Valentine’s Day Massacre”Knitting Factory, 74 Leonard St., nr. Broadway; 212-219-3132Performance artist Diamanda Galás’s “spellbinding night of tragic love and homicidal songs” should appeal to those with a gimlet eye toward the holiday.