"µ" is Greek for "M" so it should be Micro DAC, not U-DAC. Sorry about that.
I'm using it in Class A right now with the Beats by Dr. Dre Solo HD. Holly cow! this thing sounds GREAT!
[ame=http://www.youtube.com/watch?v=3vCiMTzTUtM]"First Look" Wyred4Sound µDAC-HD headphones amp/DAC unboxing - YouTube[/ame]
24 hours later:
The headphones out on this sounds very dynamic. So far, I've used the V-Moda M80 & Beats by Dre Solo HD and both sounded the best I've heard from a USB amp/DAC combo. I'm gonna throw the MrSpeaker Mad Dog and a few other cans at it and report back.