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.

I second Timrhu's recommendation of the PS Audio DLIII. A very musical dac, especially for the price. Haven't heard the EE Minimax.

Bryon

x3 for the PS Audio DL III

The Cambridge is very good and very flexible.The Citypulse DACS are also great sounding and add a headphone amp/variable output remote controlled preamp as well.
If USB is not required,The Musical Fidelity A 3-24 is built like a tank and is very musical!

I second the MF A3-24, had one for several years, very smooth and warm analog sound w/ very classy treble. Very solid 29 lbs. I currently have the Benchmark HDR, cost 4 times more but only a tiny bit better in sound but I needed its XLR for my new amp.

Gots to second the EE MiniMax. This thing is the bomb! One swinging little unit with lots of rhythmic drive. Me like.

Get the Arcam rDAC or used PS Audio DLIII. Both MUCH better than the DACs you listed.

...and I third the EE Minimax! Beautiful sounds coming from this baby! Get a hold of Bill at Morningstar!

What about the Bel Canto DAC2 or the North Star DAC, any thoughts on those two?

Bel CantO DAC 2 used is in that range. Very good unit.
Invest in good digital cable.

I briefly owned the Bel Canto Dac2. While I thought it was a good sounding dac, it was easily bested by the PS Audio DLII. ANd as mentioned above, the DLIII does provide balanced output which takes it up a notch. Something I found annoying about the Bel Canto dac was the input and outputs on opposing sides. It was a pain to place in my rack. A minor quibble but it bugged me.
The PS Audio also offers USB input. I haven't used it but it's there.

I'm delighted with my PS III running balanced.

Im very happy with my Bel Canto Dac 2,no USB,but very musical in my system