We sell the waveterminal. It's used with our professional test kits. I use the waveterminal on my PC. It's very good and I've had others buy it and exclaim it's the most fantastic thing ever. I don't know about it being that fantastic, but there is no comparison to the sound cards in my computer--it's in a totally different league. Unfotunately, I can't offer you direct comparisons to the other options you mentioned.
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?
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?