Tchaikovsky declared he had put his "whole soul" into Symphony No. 6 ("Pathétique"), and tonight at 7:30 at Severance Hall, pianist Daniil Trifonov will perform the piece, part of a program of Russian masteripeces featuring guest conductor Michael Tilson Thomas. Performances also take place at 8 p.m. tomorrow and 8 p.m. on Saturday. Consult the website for ticket prices. (Niesel)