TAKING an all too short break in the middle of the afternoon from an otherwise punishing schedule, Keeping Posted sat in with some other perceptive types at the Hilton lobby lounge, there to nibble dainty sandwiches, sip Earl Grey tea and savour the wonderful Bach and Mozart being served up by the Lauda Amadeus String Quartet. The young musicians, led by viola player Choi Poon-kai, who was born in Hongkong and has been away for more than 20 years, were discovered for their Hongkong debut while busking at London's Covent Garden. Before they knew what, they were on a plane to Hongkong and viola! - adding a classical touch to afternoon tea (at least until April 18). As the music played serenely on, someone at our table couldn't contain himself anymore. ''If music be the food of life,'' he intoned reverently, ''give me the taste of Beethoven any day.'' The perfect cue, I thought, to make my excuses and return to my computer terminal.