fladd wrote:..., one has to come to the conclusion that one of my two Focusrite interfaces is not functioning correctly (since my measurements are off by ~ 6 dB). What I am trying to achieve is to figure out which one.
Okay. I'm clearer now about your concerns. However, if one preamp was not functioning correctly I'd expect the fault to be obvious and significant, not just an apparent small difference in overall gain.
From what you've said, Focusrite acknowledges that the two interfaces are designed to have different overall max gains, but there seems to be some confusion over which is which.
I would not understand what the point of analogue gain is in the first place (or even more so, why most people want a lot of it), because you can always increase the signal in the digital domain after recording it. Why would one need a preamp at all then?
The analogue preamp raises the very small microphone signal up to a line level suitable for the A-D converter to handle. Without the analogue gain stage, the mic signal would lie too close to the nose floor of the converter, and would have a very restricted dynamic range. Boosting the level in the digital domain would also boost the converter noise floor, and you'd still have a poor dynamic range.
In other words, it's about gain staging to maximise the dynamic range capability and minimise unwanted noise.... And James has said it in fewer words while I was typing! ;-)