Within a given DAC budget (say, ~$5k) I'd go with a used ref. model - even if it's quite a few years old - rather than a new "mid-level" ditto. From my chair the DAC chip evolution, with a few exceptions, has if not stagnated then moved very slowly over some years now. The real culprit is its implementation, the quality of the analogue output stage, PSU and overall construction. Some recent DAC chips, like the dual-board chip from Hypex, provide for a staggering resolution and transparency, but I find it comes at the expense of tonal authenticity - i.e.: it robs tonal richness to my ears, even if it possibly cuts away what's considered excessive "fat" and which then that calls for substantial re-tweaking of acoustics (less absorption), speaker placement, etc.
