Low gain dac!

You think where the volume knob points matters. It does not.

that is wrong... just plain wrong. You can google around for the technical explanations, but it is a well known fact acknowledged by any competent designer that operating a system with a lot of attenuation is not good.

My rather complex desktop audio system has gain issues. They first emerged when I went from delta-sigma DACs outputting 1.9V to a NOS DAC outputting 2.5V. Gain issues worsened when I went from that NOS to another NOS w/3.0V output. 

There are all kinds of workarounds, and it's true that some volume pots are more linear at the extreme low/high setting than others. But I concluded that too much gain causes problems that are not easy to resolve downstream. I also know that a balanced DAC (which might be desirable for certain technical reasons) is impossible in this system: a DAC output 4.0-4.5V would wreck me.

@herman, 
You are correct.   Another common issue is poor  L/R channel balance when the volume control is  severely restricted to the very low positions.
Charles 

Is it possible for your pre to be sent back to the builder to have a separate gain control installed?  The reason I ask this,is myself and a few others here own Aric Audio tube preamps, and Aric installs a gain control on the rear of the unit. It is an awesome feature that I use whenever I swap in an amp with different sensitivity’s.