The pre-recorded voices should progressively get louder, with more reverb, distortion, and low-pass filter, to show that Christopher feels that he is being bombarded with information - he cannot ignore small details due to his condition, and so has to process it all, and is overstimulated as a consequence. These sounds would be partially-diegetic for Christopher only. Speaker placement - on stage.
LIVE THEATRE: At the end of "Cabaret", there is a reprise of the opening number, except it is performed in a forced, harsh manner and the orchestra is playing in a distorted, dissonant way. This is to show how society feels pressured and stressed under the watch of the gestapo, and how Clifford feels overwhelmed and shocked at the sudden turn of events.