Crossroads Music, the shop at Amagansett Square offering instrument sales and repairs as well as lessons, has long been a nexus for the South Fork’s thriving community of musicians and singers. From coffeehouse-type performances and open jam sessions to the “On the Air” events, in which Cynthia Daniels, a Grammy Award-winning producer and engineer, recorded ensembles for later broadcast, the shop has proven an invaluable resource for musicians.