Cellist Andres Diaz and violinist Nigel Armstrong will head the guest-artist roster for the 2018 St. Augustine Music Festival held on June 21-23 and 28-30. The virtuoso guest string players will be showcased in works by Bach, Haydn, Schubert and more. Armstrong, whose past performances have won him many fans, will be featured on opening night, June 21. He's emerging as a dynamic and creative artist both within and beyond the realm of classical music.  Diaz, a member of the…