It's easy to do - the pot can be switched out of the circuit.
Wouldn't switching the pot out of the circuit change the level from whatever you've just selected using the pot ?
When you turn the gain knob on the 7xx, it displays the amount of gain in dB (does the m10 do that?).
No - there's nothing on the display. If you need to know the absolute value, you have to look at the knob itself (not hugely easy in the dark!)
I'm not using an external pre, and hence it presumably makes sense to have a gain control acting on the analog signal before it hits the built-in pre.
I imagine in expensive units, this gain control could be
digitally controlled. But I fear in some cheap units, the gain into the internal pre may be fixed, with the gain "control" adjusting the signal in the digital domain,
after the pre and A/D stages. Not so good.
Again, I'm talking about using internal pre. I agree things are different with external pre.