DACs: Airport Express vs waveterminal vs mini-dac


I know this is impossible to quantify, but with a good stereo system (Cayin TA30 tube integrated amp & Green Mountain Audio Europa speakers), what's the magnitude of difference using the following dacs?

Airport Express (I already have the AX, and can connect it to the integrated amp with RCA's [analog])

Waveterminal U24: computer to USB to waveterminal to amp (waveterminal does the DA conversion)

Inexpensive DAC like ART DIO with waveterminal: computer to USB to waveterminal to ART DIO to amp (ART DIO does DA conversion)

Apogee mini-dac: computer to USB to mini-dac to amp

Other?

What's the best bang for the buck?
mschamberlin3865
Followup:

I was in on this thread earlier on and wanted to let everybody know where I am now. I did buy a U24 to use with my G4 iBook. I purchased the Apogee Mini DAC and have my Sennheiser HD650s connected to the Apogee via XLR outputs through a balanced Zu Mobius cable. I listen almost exclusively to classical music and am a professional musician. This setup is astounding. I can't stop listening.
I am using the U24 as well, with nice results. But I want more. I am trying to decide between the Apogee USB Mini DAC and the Benchmark DAC 1. Any opinions or experience?
I just figured out that I can get lots of great radio through my computer/internet as well. I can now sell my changer and tuner if I want. I am thinking about putting my money towards a really good DAC since my computer is turning out to be the heart of my system. Now that I have ripped my 500 cd's to computer, and have all the album artwork loaded as well, I can't believe I didn't do this sooner. I am rediscovering my music collection and listening to stuff I haven't listened to for years. It would not surpise me if we begin to see a lot of USB DAC's on the market very soon.
I answered this in the Digital thread, but I have the same setup as you and I think you can't go wrong with either the Apogee or Benchmark. I own an Apogee Mini DAC and it produces an incredible sound. I am using it with Senn HD650s with a Zu Mobius cable which has been terminated with XLR plugs to go directly into the DACs XLR outputs. If you are using headphones, I recommend the balanced plug. However, the 1/4" headphone out on the Apogee is really excellent as well, I was surprised.

dshea
PC, wireless to SB2.
SB2 -> External DAC or Analog out. Up to you.
SB2 will server as a bit accurate transport.