Alright, with 20 hours under my belt of listening I'm shipping this guy back. I'm not getting the changes to the signature I was hoping for.
To be clear, it actually sounds pretty fantastic with my Thunderpants... not quite to the level of O2/ODAC - it's just a bit lean/flat by comparison, but just a bit, which is pretty outrageous considering it's entirely USB bus powered. The DAC portion to my ears outshines the ODAC and running the Dragonfly -> O2 is absolutely stellar - very detailed, lack of digital hash, dynamic, tight, crisp... a dynamite pairing, both with the Thunderpants and EPH-100.
But that's not what I bought it for, and with its headphone out -> my 16 ohm EPH-100, which to be honest are warm by their nature, it just pushes things into an unsavory territory descending into mush. If I were rocking a leaner and/or higher impedance BA IEM I'm sure it would be sublime, but I am rather attached to a minimal setup and find the EPH-100 a very good match for my sonic preferences. With it I even prefer the headphone out of my Macbook Air to the Dragonfly, and doing some research I now understand a bit more why.
I spoke with Alasdair at Audioquest today, (I lost the USB Cap already... ) He and I got into a "Burn In" conversation. The view of the AQ folks is that the Dragonfly should be at its best after 150 hours of so of burn in. So sending it back after 20 may be premature.