Best DAC under $ 2,500 on used market

Haven't heard an Esoteric X-03, but I had a Bel Canto DAC3VB in my system for a while and it was to say the least excellent (if I could've afforded it, it would still be here). It's very good on its own, but with the VBS power supply it goes to another level entirely. Transparency, micro/macro dynamics, 3D soundstaging, tonal nuance, and a quiet backdrop are among its strengths. If you can find one used it might be in your price range, and it's hard to think you'd be disappointed. Best of luck.

Just noticed this post was from 2008. Ugh.

I 2nd a PS Audio PWD MkII with bridge and don't forget to replace the fuses with HiFi Tuning Supremes. Like computers, it's remarkable how much you get for little $$.

If you are looking for used, try the Luxman DA-06