Low volume listening is usually not that great with a DAC direct to amp.
Simple fix
Most likely because it was "bit stripping" (lower resolution), for digital domain volume controls in dacs to give all bits (resolution), they need to be at or over 70% in volume, if this is too loud for you, simply insert a $49 Schiit Sys passive between the dac and poweramp.
Set the Sys volume control once only with the dac at 100% so you’ve got just over the loudest you’ll ever need, then back off the dacs digital volume, so then you’ll use it as the master volume in the top 1/3 of it’s volume range.
Cheers George