My vote in the used 300-500 price range would be for any of the monarchy m22* dacs. Very nice and big improvement over the internal dacs of my pioneer dv45a using an m22c.
Best Inexpensive DAC
In the last 12 months I have mananged to purchase a used ML27.5, used ML38S and a new pair of Thiel 2.4. I am broke, but I can't stand listening to my old Denon CD player form 1992. I do have a coax digital out on the unit, so I thought of purchasing an interim inexpensive DAC to get me by until I can get something a little better. Any suggestions?