Thanks Kevin....Oh right thank you. it says this in the operating instructions...
Power amplifier direct switch (power amp direct)
This switch is used to listen to the sound from a component connected to the "POWER AMP DIRECT" terminals. When this switch is pressed inward to the "on" position, a superior level of tone quality can be obtained., because the signals from the component connected to the "POWER AMP DIRECT" terminals are sent directly to the volume control and power amp section of this unit. The mode selector, loudness switch, balance control and tone control circuit are bypassed.