Above, from left, Suhail Khoury, Ahmad Al Khatib, Ibrahim Atari and Yousef Hbeisch performing at the Kennedy Center in Washington in March. By DANIEL J. WAKIN WISPS of mournful tunes from a cane flute mingled with the plucking, jangling arabesques of the zitherlike qanun, the oud and gentle drums. The sounds arose from a quartet of Arab musicians who call themselves the Oriental Music Ensemble as they shared a precious moment of togetherness in the Miller Theater at Columbia University in