Your analog noise floor is limited by thermal noise anyway, so if you use analog volume control it doesn’t get any better. Analog volume control just adds it’s own distortion and noise on top.
And the most stupid thing is that “pre-amps” are “pre-atts” these days. So if you set preamp to -20 dB volume and typical power amp gain is 36 dB, then the net gain is 16 dB. But you just lost 20 dB worth of dynamic range by shuffling the gain back and forth. It would have been better to just have 16 dB of gain to begin with in first place. Then the power amp wouldn’t be also amplifying the noise by unnecessary extra 20 dB.
Low noise DAC can output correct level for the power amp, and the noise floor is well below that of the power amp.