Apparently they want you to run the amp wide open with this box in front of it. That's a formula for poor noise performance, never mind all of the specious audiophile claims.
yeah, I couldn't agree more. Though some folks claim that they can find the "sweet spot" gain range of their amp, and control the volume with these so called "passive preamps."
I am guilty of using one for a different purpose. My 1982 QSC 1100 has a gain knob for each channel. For convenience I use the single knob of the "passive preamp."
I am guilty of thinking I have found the magical sweet spot of my system many times. Usually it is after a few beverages. In the morning the system sounds completely different. Auditioning equipment is difficult, way to many perception influences and variables. Ah, but this is what makes life interesting! Variety is the spice of life!