There, I've simplified the syntax now, it's better. The poem pivots on lines 7-9. I think it's OK... The opening octet focuses on the (only half-believed) "logic" of supposedly "winning over" the torture victims (making them sing in unison). The sextet discounts all that, replacing it with the more basic goal of squeezing out useful information. The final couplet underlines the greater folly, the more egregious illogic, of the whole process.

This idea of making prisoners "sing" is sort of a Hieronymous-Boschian parody of the "attunement", the spiritual "octave", alluded to in previous poems (posted here over the last few weeks & months).