There are some extremely powerful amps that are designed to be run with 3 phase power. This one is digital and is pretty small. Digital amps can be very efficient. It is for stadiums and other industrial applications.
Yes it is for stadiums and big installations. There was already some ~20KW amps on the market made by LabGruppen and Powersoft (they are single phase 230Vac) but this PKN is something new with three phase 400V powering.
400V three phase operation + state of the engineering = great power in compact size