The boxes were a separate room, isolated from the courtroom, for witnesses and accused who shouldn't be influenced by the proceedings in the main courtroom. That wouldn't stop Max from being able to hear the thoughts of the people in the next room, but the thought was there.
Listening to Nico's thoughts was much more entertaining, as she was taking the role of prosecutor as Second in Command of the Terminus Trading Company. She pulled no punches with her questioning, and their actions actually sounded worse coming from her deceptively innocent voice setting than when Max read them for himself.
All but the four Company Captains pled guilty and pleaded for leniency, asking to be dismissed and sent to Rae 5 for hard labour instead of given the death penalty as mutineers.