Mine is kind of similar.
I have an iMac running AIFF files and use via Toslink the Apogee Mini DAC which goes straight into my power amp, so far I've not noticed any quality issues with the volume control built into the DAC (although it is an analogue control on the Mini). I have connected the DAC to my passive pre-amp and set the output at 'fixed' but the sound was indifferent.
However, seeing as the Duet is a digital volume control then it may have qualitative issues, but until you do a direct comparison you won't know for sure. Saying that on my Mini I tend to set the gain at a certain level and use the volume control on iTunes as I can then control it from my sofa (wireless keyboard - world's most comprehensive remote ), again I haven't noticed any quality problems although the sound does become more open once a certain level is reached, having said that it could simply be the minimum level where my system gets into its stride. It was much the same when using a CD player and the passive to be honest.
If you want you're quite welcome to borrow my passive pre and try it, but you may have impedance mismatching issues, not a problem in itself, but it can limit the top end frequencies.
Ben Duncan mains conditioner
2022 MacBook Pro 14" M1 Pro 10/16/16/16
Samsung QE75Q90T 75" QLED TV
XMOS DSD Async USB to Coax converter
RME Audio ADI-2 FS (AK4493) DAC
Chord Clearway XLR interconnects
Audioquest Crimson USB interconnect
QED Quartz Reference optical interconnect
Edifier S3000 Pro active speakers
Atacama SE24 stands