Best used DAC around $500

PS Audio DLIII is a good bet at your price point. I was looking for a more esoteric dac for my Mac Mini but "settled" on the DLIII and am very happy with it. Not looking anymore.

New Eastern Electric Minimax DAC - $750. - This was just emailed to me by a friend that I recommended the very same DAC.

This weekend I finally got the HiFace and a Black Cat BNC cable...and got everything hooked up. My config is RCA Analog out of the EE Dac to my pre-amp via a Cardas Golden Cross (my personal favorite interconnect cable). Long story short, the sound is absolutely stunning. I did a bunch of A/B comparisons with my other sources (Sony XA9000 ES SACD player, etc). There is a tiny bit more detail with the Sony player...albet in a very cold, thin, clinical manner vs the EE...the warmth and soundstage width of the EE blew away anything I have ever heard in my system. Music suddenly became much more emotionally involving. The difference was not subtle...it was huge! Some of my High-Res files through the EE litterally put me inside the jazz club. This is exactly what my Krell/Revel set-up needed. Again, thank you for turning me on to the EE. It is the best addition to my Hifi system in a long time.

I use a Moon 100d which retails new for $600. Very nice.