I do prefer the O2 sound ever so slightly. With no way for me to properly ABX the 2 amps, it's really difficult to make any solid recommendation of one over the other with any degree of confidence. The build quality of the O2 from JDS Labs is wonderful, but the device itself is cheap. All of the connections are on the front panel, including the power, input, and output; which makes things cluttered and more difficult to manage. The input and headphone jacks are 1/8" and they are not rated particularly high with regards to the number of insertions they can handle. It's built superbly, but it's fundamentally designed to be inexpensive, and this shows. When the new ODA version is available, I am going to see if I can pay extra for better headphone and input connectors.
The Asgard has the RCA inputs in the back, a full-sized 1/4" headphone jack in the front, and the volume knob is much larger and easier to fine tune to an ideal listening level. It's like a tank, and the build quality is equally great. I highly recommend both amps.
Pure sound quality: O2 barely outguns the Asgard in my opinion, and most notably at high volume levels, but still not an overwhelmingly obvious improvement.
Build quality: Asgard has an advantage when compared to the much smaller, lighter, and seemingly cheaper components used with the O2
Again, if you can benefit from a much more compact amp, the O2 sounds as good or better to my ears than the Asgard with my Denon D5000. That said, the Asgard is an awesome value, I still use it as my main amp for home, with the O2 serving duty as my amp of choice in my office where I work.
