I've tried to concieve of a simple test to make sure my input meters are reading correctly and I think I came up with one. Let me know if this all looks legit Nick.
A Lynx staff member said the following about the Aurora 16 A/D and D/A:
"The maximum level of 0dBFS at +4dBu trim setting is +20dBu (16dB of headroom)."
So I took a stereo output from the Lynx into the H7600 and outputed a sine wave from Logic at -0.1dB just so I don't clip.
That means that I can subtract 16dB of that going into the H7600. The H7600 reads at -9 with 6 LEDs lit.
Now 9+16=25dB, which corresponds to the 25dB of headroom you spoke of.
I think this shows what I'm looking for: that my LEDs on the H7600 are working probably and it shows simply the mathematical relationship between the output of the aurora and the metering on the H7600.
Is that right? It's kind of hard to wrap my head around when I think about it. I'm hoping this isn't all just coincidence that the numbers add up.
So it must be, as you said, that my X-Desk really does have a low gain structure, because it seems so far difficult or near impossible for me to get up to -9 on the H7600 through the X-Desk without the X-Desk hitting the read somewhere in its signal path.