I posted something about this DAC on the HD800S thread, I'll copy here for those who are interested....
Apogee Groove vs Audioquest Dragonfly Red:
So far, I have tried the HD800S with two portable dac/amps, the Apogee Groove and the Dragonfly Red. I came away with the following conclusion after extensive A/B testing. The Dragonfly Red sounds more transparent and clear than the Apogee Groove, but it doesn't get loud enough for a lot of songs I tried. The Apogee Groove sounds pretty decent, but it's a tiny bit more tame with the sound stage and also a little less detailed than the Dragonfly Red. The Apogee Groove does drive the HD800S very well, with it getting louder than I need on any music I threw on. Bass feels stronger with the Apogee Groove. I think the "constant current drive" they are using in the Apogee Grove is working pretty well for the HD800S, but the DAC is better in the Dragonfly Red. The Apogee Groove uses a 28bit ESS Sabre DAC, the Dragonfly Red uses one of the newer 32bit ESS Sabre32 DACs with bit perfect volume control. Apogee also makes a Groove "Anniversary Edition" in gold or silver that uses the same 32bit DAC that the Dragonfly Red uses, so that would be the best of both worlds - but they charge a ridiculous $600 for it, double what the regular Groove costs. I would grab the anniversary edition in a heartbeat if I found it used for around $300. I have settled on the regular Apogee Grove as my portable solution to use with my android phone and the HD800S.
Anyone own the anniversary edition with the improved DAC? If so, how does it sound compared to the regular? Can't seem to find one of those used anywhere...