With Ralph Vaughan Williams’s Sinfonia Antarctica and Symphony No. 9, Martyn Brabbins and the BBC Symphony Orchestra bring their Vaughan Williams cycle to its magnificent conclusion. These two symphonies date from the composer’s later years, and, while initially misunderstood or underrated, both scores are teeming with creative vigor, startling orchestral color, and absolute mastery of symphonic thought, all qualities which abundantly inform these marvelous performances.