Many dacs don't have any means of volume control, others strip bits. In order extracting maximum potential from these dacs requires some form of volume control, the quality of that volume control has major bearing on sound quality of that dac.
This is true if your goal is to get the music as close to the original recording as possible. The Benchmark DAC3 paired with the ABH2 power amp will get you state of the art transparency for $5000.
However, many of us would be in for a rude awakening with that level of transparency in our systems. Our tube preamps and R2R DACs add flavor or color to the sound...giving us a deeper and wider soundstage, additional layering, and weight to the sound...the perception of 3D sound.