How should the channel level indicator be used when adjusting the input? Conversely, how should the master level indicator be used when adjusting the output? Also, up to how many dB can the unit output without distortion?

Adjust the TRIM control so that the channel level indicator lights around 0 dB at the peak level of the input audio.

Similarly, adjust the MASTER LEVEL control so that the master level indicator lights around 0 dB at the peak level of the output audio.
When MASTER ATT. is 0 dB, output without distortion is possible up to 21 dB.
When digital clipping occurs internally, the CLIP indicator will flash quickly.

*You can lessen the occurrence of sudden, unpleasant digital clipping of the master output by setting [UTILITY] > [MASTER LIMITER] to ON.

*Use [UTILITY] > [MASTER ATT.] to appropriately set the attenuation level of the audio output from the MASTER 1 and MASTER 2 terminals to match an acceptable input level of the device connected at a subsequent stage.