Here are some classical recommendations from founding BLASPHEMY member - former bassist and current vocalist - Nocturnal Grave Desecrator and Black Winds. They were listed in an interview with Polish zine Holocaust in 1990.
Yes, pick up some good classical like PROKOFIEV ("Alexander Nevsky Cantata", "Scythian Suite"), STRAVINSKY ("Rite of Spring", "The Firebird"), MAHLER (Symphonies V and VI), MUSSORGSKY ("Night On Bald Mountain", "Pictures At An Exhibition"). I recommend this stuff for any Black Magic Occultists, Satanists, are any BLASPHEMY intros, effect listener.
Nocturnal Grave Desecrator and Black Winds / Blasphemy interview, Holocaust #4, 1990
Prokofiev: Alexander Nevsky, Op.78 (Yuri Temirkanov, St Petersburg Philharmonic Orchestra)
Prokofiev: Scythian Suite, Op. 20 (Abbado, Chicago Symphony Orchestra)
Stravinsky: The Rite of Spring (Leonard Bernstein, London Symphony Orchestra)
Stravinsky conducts The Firebird (final three scenes) (New York Philharmonic)
Mahler: Symphony No. 8 (Bernstein, Vienna Philharmonic Orchestra)
Mahler: Symphony No 6 in A minor (Bernstein)
Mussorgsky: Night On Bald Mountain
Mussorgsky: Pictures at an Exhibition (Sir Georg Solti, Chicago Symphony Orchestra)