Disable preamp function of Audio Aero Prestige

I wish to disable the preamp function of the Audio Aero Prestige player. Any experienced hand who can shed some light? Appreciated.

FYI I contacted a FM tuner to the unbalanced input of the Prestige and the player sings like hell. I no longer used it as preamp. I wonder if disabling the preamp function would make a substantial improvement in sound.