The Hongkong Philharmonic, with William Preucil, violin, Cynthia Phelps, viola, Ronald Thomas, cello, David Atherton, conductor. HK City Hall Concert Hall. ONLY one work from the penultimate ''Atherton And Friends'' series will remain absolutely memorable: Sir Michael Tippett's Triple Concerto for violin, viola and cello. The reasons are manifold. First, Atherton has had a special musical relationship with Sir Michael, the composer effusively praising the conductor in his recent autobiography. Second, it is rare to get three such fine soloists together for such dangerously complex work. Most essential, though, is that the then 70-year-old Sir Michael wrote an astonishing paean to ageless wisdom rather than a last clarion call. It would be platitudinous to say that Sir Michael's powers have increased with age. Rather, after this first hearing, they have deepened. His few familiar tricks - a few measures of jazz, the stockpiling, rather than development of themes - are all here. But the Triple Concerto has both an aural and philosophical content which shows a composer at the height of his powers. For such an eclectic man, Sir Michael could well have sub-titled the work with the title of American writer Ralph Ellison's collection of essays on the black experience, Shadows And Reflections. Aurally, the orchestral sounds reflect themselves, reverberating at times to the softest or more brazen sounds. Fanfares become lullabies, orchestral consorts echo around the orchestra. Yet the three solo instruments seem to proceed at their own pace. The most beautiful touching slow movement is played almost entirely with a bass oboe. Outside movements are similar to Sir Michael's Concerto Grosso yet with a deeper, less formalistic tone. The music was challenging enough for a Hongkong audience but after 45 minutes without a single break, the power of the work was only augmented. Credit must go not only to the soloists but also to the orchestra, which appeared to play the sometimes impenetrable music with clarity and understanding. Atherton started the concert with an honestly trenchant account of Beethoven's Creatures of Prometheus overture. But the conductor never considered a smaller, ''period'' 18th century orchestra. The entire Hongkong Phil played it with Mahlerian grandeur. It isn't great Beethoven, but lyric and fanfare had an honest splendour. For Richard Strauss's, Le Bourgeois Gentilhomme suite, one felt embarrassment. Atherton had shoved the first chair strings to the back so his visiting ''friends'' could play their solos. The pared-down orchestra played well - with wonderful solos by pianist Shirley Ip and trumpeter Judith Saxton. But such an arrogant insult to the Phil's string players would, in any other orchestra, have caused an immediate walkout.