I think of digital volume control as the digital signal being altered which is something audiophiles seem to go to great lengths to avoid.
I think of analog volume control as signal attenuation which narrows the gap between the signal and noise (i.e. reduced signal to noise ratio) which is also not desirable in the next stage of amplification.
I think the pro audio rule of thumb for gain structure is to have the input signal as high as possible to maximize the signal to noise ratio (I might be saying this incorrectly).
With these things in mind, I would try to set everything to "zero" and let the preamp do its job.
This is one reason that I had a DAC that doesn't have any volume control and set my bluesound node to have a fixed output level.