MUSSORGSKY: "Songs and Danses of Death"; arias by Rimsky-Korsakov, Borodin, Rubinstein and Rachmaninoff. Dmitri Hvorostovsky, baritone; Kirov Orchestra; Valery Gergiev, conductor. Philips 438 872-2. The young Russian would seem to be on a roll. Following his splendid "Onegin," here is a brilliant collection of mostly unhackneyed songs and arias. The perfectly equalized, multicolored sound may be a bit light for Mussorgsky, but his delivery is blazingly dramatic. He brings the same commitment to the arias, especially excerpts from "The Demon" and "Sadko." The "Igor" aria lies rather low for him, but he manages a thrilling climax nonetheless. Evident everywhere, but most notably in the "Aleko," are exemplary enunciation and extraordinary breath control. Gergiev and his orchestra provide a cushion of supportive sound any singer might pray for.