A performance of the first, and most dramatically effective, version of Modest Mussorgsky's 'Boris Godunov', an opera with a long and sordid revision history.   With the participation of conductor Kent Nagano, Spanish stage director Calixto Bieito proposes an original reading of this brilliant work.   'The bass Alexander Tsymbalyuk sings Boris with handsome, lean tone and ably conveys the czar's mental disintegration' -  New York Times