Possible Clues:

• Villa-Lobos's "Bachianas Brasileiras No. 5" is scored for voice and eight of these
• Big strings
• Largely with strings attached for the prisoner, so it's back
• Instruments for Rostropovich
• Largely a matter of strings for the prisoner thus back
• Small room, very large instruments
• Orchestra group
• Ensemble of eight in the score of Villa-Lobos' "Bachianas Brasileiras No. 5"
• Violins' kin
• Sizable strings