Multichannel treatments of older rock recordings that truly serve the musical essence of the original are rare. Here’s one that does. The “You” of Wish You Were Here, Pink Floyd’s ninth studio album, is Syd Barrett, a founding member of the band and superb vocalist and guitarist who left the group because of a psychological unraveling, possibly drug-induced. Recorded at Abbey Road over six months in 1975, Wish You Were Here has an elegiac quality throughout. It’s best experienced in a straight-through, 45-minute sitting. The two big sections of “Shine On You Crazy Diamond”—both with long instrumental sections—frame three other songs that touch on the record’s other theme, a harsh indictment of the music business. “The name of the game, boy, we call it riding the Gravy Train,” sings the record company executive. James Guthrie’s 5.1 mix generates a vast sound space. Surround effects are imaginative— at one point, all the action collapses into the right rear speaker—but bass, drums, and lead vocals are firmly anchored in front. Guitar and synthesizer sonorities are complex and rich; baritone sax is exquisitely textured. The mechanical pulsing that begins “Welcome to the Machine” is harrowing in its visceral acuity.