Possible Clues:

• Ma or Casals
• Jacqueline du Pré, for one
• Musician in prison?
• Yo-Yo Ma, e.g.
• One takes a bow, still shaky after church
• Where there's a prisoner, sit when he's playing
• E.g. Casals, du Pré
• Yo-Yo Ma, for one
• Player is put in room inside, with temperature reduced
• Musician beyond room is German