Any performance of Britten's War Requiem becomes a special occasion. To play it on the final day of the Aspen Music Festival only added to the glory. David Zinman conducted the Festival Orchestra plus a legion of additional musicians Sunday in 90 minutes of the most intense, powerful music-making of the summer.The warfare in the world today only underlines the message in Britten's idiosyncratic interweaving of the Latin requiem mass with World War I poems by Wilfred Owen, who as a British soldier was killed just before the armistice in 1918. Owen channeled his outrage at the war into poems that stressed the humanity of the combatants. Britten's music makes us feel the emotions, and Zinman led a beautifully proportioned and deftly paced performance.Tenor Anthony Dean Griffey, who sang superbly in Britten's Serenade only two weeks ago, lavished his warm, plangent sound on Owen's poetry. William Dazeley sang the poetry with great depth but without overacting. His baritone made a smooth fit with Griffey's tenor. This was especially apparent in their duet in the Agnus Dei, when their voices harmonized to represent the angel interceding on Isaac's behalf as Abraham prepares to sacrifice him.That's one of the most moving moments in the piece. In Owen's poem, Abraham ignores the angel and sacrifices Isaac, to reflect the soldiers' sacrifice. That, and the glorious, quiet finish, in which Jane Eaglen's soprano sailed over the mixed chorus and orchestra on a final repeat of the Requiem stanza, had me choking back tears.Eaglen, whose final scene of Salome last week was sabotaged by faulty balances with the orchestra, was perfectly audible this week as she sang the soprano's lines in the Latin mass with enviable purity and focus. She stood at the center front of the Colorado Symphony Orchestra Chorus, arrayed above and behind the stage. The Colorado Children's Chorale sang its music from offstage, piped through the tent's sound system, with reverb. Whoever had the idea to do that should have reconsidered. An artificial sound is not what this piece needs. It's about humanity. It's real. And the rest of it hit that mark perfectly.The Sunday concert capped a strong final week, which included a fine outing by the American String Quartet, two concerts by the Baroque ensemble Apollo's Fire, an all-Mozart recital by pianist Vladimir Feltsman and a one-act Russian opera about Mozart.For their concert Thursday, the ASQ turned to the quiet side, pieces that may not lead to standing ovations because they end softly, but demand attentive listening and, in the end, reward it. The menu included Haydn, Strauss and Shostakovich, but the grabber was Schoenberg's lushly and unabashedly Romantic sextet, Verklärte Nacht. The music came off with remarkably clarity and attention to detail.Thought not quite as gripping as his Defiant Requiem or his exploration of the psychological battle between Stalin and Shostakovich, conductor Murry Sidlin's concert drama on Mozart Friday had its moments.Without Misha and Cipa Dichter's ham-handed galump through Mozart's Concerto for Two Pianos in E-flat, Sidlin might have had more time to develop his theories of who might have done Mozart in. Actor Damon Gupton played a detective who offered seven suspects, each preceded by the "doink-doink" sound effect from the TV show Law & Order.The best parts were the orchestral excerpts, including the first movement of the Symphony No. 40, the slow movement of Symphony No. 38 and the Overture to Don Giovanni. After so much obscure, often second-rate Mozart this summer, it was a pleasure to hear some real masterpieces, or at least portions of them, and beautifully played.In the semi-staged opera, both baritone Donovan Singletary, who played Salieri, and tenor Roland Sanz, who played Mozart, sang the English translation with great conviction. Rimsky's music filters a Mozartean style through late 19th-century Russian sensibilities.In his all-Mozart affair Saturday night at Harris Hall, Feltsman seemed to aim squarely at the simplicity, grace and purity of the music. There was no artifice, and it was delightful to hear. The short solo works, especially the Fantasy in D minor and the unusually charming Rondo in A Minor, were more like warmups to the Violin Sonata in E minor and Piano Trio in E major. Feltsman and violinist David Halen were clearly on the same page for both, and Michael Mermagen added his attentive cello playing to the trio.Apollo's Fire has been getting raves for its onstage enthusiasm and period-instrument chops. In the concert I heard, the highlight was Bach's Coffee Cantata. Soprano Rebekah Camm's accurate coloratura and bubbly stage presence stole the show portraying a young woman hooked on coffee. (And this was centuries before Starbuck's, Ink! or Zélé.) Tenor Thorsteinn rbjörnsson and baritone Ted Huffman were only a step behind.The opera department completed a strong season with Britten's Albert Herring. With Robert Spano, music director of the Atlanta Symphony, conducting the music with vigor and idiomatic humor and Edward Berkeley doing his usual insightful work directing, Albert hit all the right notes musically and theatrically. The singers battled their English accents with varying degrees of success, but vocally they were good, especially in ensembles such as the nine-part threnody the townsfolk sing when they think Albert is dead.Kalil Wilson brought a silken tenor sound and an engaging and often funny stage presence as the slow-witted goody-two-shoes title character. He made a believable transformation to a young man willing to stand up to his mother and the repressive citizens of the English country town. Liam Bonner looked appropriately rakish and his burnished baritone sounded sturdy as Sid, Albert's pal who encourages Albert's growing-up with the help of some rum-laced lemonade.Finally, Alan Fletcher, president and CEO of the Aspen Music Festival, slipped one of his own compositions into the last Monday chamber music concert. His piano trio, Dreams of Rain, made a strong impression. My guess is that this is one living composer who will be invited back for more, and deservedly so.The piece, completed in 2000 while Fletcher was summering in Costa Rica, evokes the sound but even more the feeling of a lazy tropical mountain day of rain, sleep and memories of the recent past. The four movements are tinged with the colors if not the beat of Latin-American music. The musical language is tonal, dissonances tend to be soft, and Fletcher is not afraid to write a pretty sequence in contrast to something harsher. The delicately etched sounds of the scherzo and the finale invoke the strongest feelings, precisely because of their fragile qualities.