Could you recommend a nice used USB DAC?

I am looking for a nice used USB DAC.  I currently have an Arcam CD23 which I really like to but I am looking to go with the USB DAC route for high resolution streaming. 
Could you recommend one and give a short description on the sound?
It seems like there are a lot of recommendation for the Chord Mojo DAC but it seems to be a bit more on the "detail" so I am not sure it would be for me.  The reason I like the Arcam because although it has a lot of details, the musicality always comes first.
First, my preamp is a Conrad Johnson 17LS and although it's a very good preamp, it's a bit laid back so it may not reveal all the details.  Hopefully I get a new preamp soon. 

After listening to the Ayre for a few weeks now I have come to the conclusion that it probably is a better unit vs. the Arcam CD23 at least judging objectively.  I mentioned that the Arcam has a slightly better present but after comparing that to the Ayre, it think the Arcam may have a bit of a upper bass lift so to make the sound just a touch warm.  But it may hurt its bass response which was not that apparent until I compare it to the Ayre.  The Arcam bass seems slightly congested and not quite as agile as the Ayre.  Also the Ayre also has more resolution on the upper mid and treble region.  You get more treble on the Ayre and there is a slightly better trailing on the treble.  The Ayre may also have a lower noise floor although I think some of it is masked by the 17LS.  Ultimate, I think the Ayre is more neutral and sounds slightly cleaner but just as smooth.
The interesting thing about this comparison is that even the Arcam is almost 17 years old, its sound can still be compared some of the newer units.  I think it may be let down by its power supply.  That maybe why Arcam had updated to CD23T version which has a better power supply and improved bass.  I also notice that the Arcam is a bit more sensitive to power cable vs. the Ayre.
Hopefully I'll get a new preamp which should reveal more about the difference between these two players.
just go for Wavelength USB Dacs
gordon ranking is the only man you can trust in usb dans
...and he morphs into gordon  skanking when you play roots through the Wavelength