I only use a scope to check max. gain in a device before distortion/clipping.
You trying to set gains for low noise, equal output what?
Sometimes a spl meter is easiest to use for levels. :smile:
Octave analyzer is best to set levels with to tailor the response to what you want.
Knowing the highest noise component in the system at 0 source level can help determine how to keep the source at max. level above the noise before clipping.
If you can get the test tones into the head unit at a reference level that is relevant to your sources I'd determine what voltage level on the scope and volume control setting is max. before clipping and then work to the crossover, equalizer, then the amps. to be at full output before you clip the head unit.
Unless the crossover is built in then you have to work with those outputs individually.
Levels and outputs on the amps. may be set completely different due to driver efficiencies on the highs and lows.
I'm not sure what good putting test tones at ? level, into the amps. directly are gonna do for you.....