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Can someone please explain the reason and benefit of step #6? I originally set my levels with a DMM and now I’m being told to set them to minimum. What gives?

1) Set your source units fader and balance controls
to their center positions.
2) Disconnect the output RCA connections between
your DQT and the amplifier(s). . . or next
processor in line.
3) Start playing some relatively dynamic music
and set the volume on your source unit to
about 3/4 of maximum. You should not be
hearing anything at this point. If you are
hearing music, go back to step #2; if you are
hearing voices go see a doctor!
8
4) Starting with the DQT “Input Level” control,
increase or decrease the control knob until the
“Input Maximized” LED begins to flicker
steadily with the music.
5) Now adjust the output level control until the “2
volt” or “5 volt” light starts to flicker. You will
want the output voltage to match up your
amplifiers input gain levels. If you don’t know
how much this is, ASK the amplifier manufacturer
or read the owners manual of the amplifier.
6) Very Important - Set the input gains on the
amplifier(s) at minimum!
7) Double check that you performed Step #6
8) Decrease the volume control on your source
unit and re-connect the RCA’s between the DQT
and the amplifier(s).
9) Now increase the volume on your source unit
to your normal listening level. For some of you,
this may be louder than others!

Because most amplifiers have a set input they are capable of handling and setting it to minimum is the "safe" way to do it to avoid clipping.

Thanks. Should I set it to minimum or stick with the DMM setting?

also: DQT has a line-driver for the output stage.