If the MASTER OUT [ATT.] is set to 0 dB, the output won't be distorted with the volume up to +25 dBu for the MASTER1 output (XLR) and +21 dBu for the MASTER2 output (RCA).

Adjust the [ATT.] to set the attenuation level of audio output from the [MASTER1] and [MASTER2] terminals.

When the [PEAK LIMITER] is enabled, you'll be able to alleviate sudden, unpleasant digital clipping of the master output.

For details, see [Changing the settings] in [Settings] in the Instruction Manual.

You can read the Instruction Manual [here].