Hong Kong Bach Choir, City Hall Concert Hall, Thursday, December 11 Christmas belongs to choristers. At this time of the year they emerge from months of rehearsal to gladden winter's sadness and delight us with their melodies. Given that Hong Kong's rich choral heritage has suffered a rather precarious and insecure history, the Bach Choir stands as a refreshing oasis in which the great works flourish. The two masterpieces presented by the choir and the Hong Kong Sinfonietta on Thursday evening under Jerome Hoberman's careful direction were Stravinsky's Symphony of Psalms and Mozart's 'Great' Mass in C minor. The Stravinsky, by adding two pianos to its large orchestra, redefines what we expect of symphonies and psalms. Hoberman led his disciplined forces through Stravinsky's astringent harmonies and perilously exposed melodic lines with sure authority. Always uncomprising, Stravinsky treats voices as if they were instruments and it is to the choir's great credit that they took up the challenge and emerged triumphant. Challenges of an entirely different order awaited their performance of Mozart's Great Mass. This masterwork is like a sculpted torso whose absent limbs may have never existed. It is a delicate and subtle piece that requires a great deal of and precision. Sadly, such large forces made Mozart's light textures and dance rhythms too often heavy and overwrought. The most satisfying performances came in the full-blooded fugal movements, shining with a bright forward tone. But none of the soloists seems really at home with the liturgical-oratorical repertory. Though she negotiated many of Mozart's melodic lines with ease, soprano Katusha Tsui-Fraser still has trouble pronouncing Latin and not once did bass Albert Lim Chun lift his eyes from the score. This great repertoire enjoys a large audience and the Bach Choir under Hoberman's direction is a worthy guardian of its treasures.