I tried it with several systems, the firstone was a Scarlett 8i6 1gen, second with Audient iD14 MKII, third Audient ID44 mk2, finally a 16 channel motu16A system, connected to a sennheiser rack (I don't remember the model) and finally an output 16ch ADAT.
Everything was measured with a Behringer ECM8000 always connected to the first input channel of the sound system.
For the reference signal take output 2 sending it to input channel 2.
In all these measurements I had that problem with the gains, they were always low and I had to turn the volume up to the maximum.