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
I use the UA-5 and it sounds pretty good for its price and never causes crashes...
Where do you live? I'm sure someone hear that lives near you will let you borrow their Mac.
FWIW the m-audio audiophile firewire has worked flawlessly from my iMac. Sound is not as good as from my CD player, but is fine for background music use. One day I'll upgrade it, but, it works fine. I've also been using it to slowly import my LPs into iTunes.
I live in the mountains in central Oregon. 7 miles to the nearest town of 1000.
Surely someone with a Mac can make the drive. Anyone?

I'm in Colorado now, occassionally in the Bay Area, but not anytime soon.