The lack of function confused me as well; I had just performed a fresh install of Win 8 Pro and Mac OS X Mountain Lion, and I know the USB ports work on my motherboard and case because I used the Recon3D USB with them before (and a new Recon3D USB with them now, though I notice I have to unplug/plug in the new one a few times for Win 8 to recognize it). At the time, I just attributed it to something going wronged with my OS installs, but the custom PC is just for gaming currently and I bought a new Mac Mini that has all my music on it (and so does my 30GB iPod Video).
The ODAC was created after it's designer was banned from Head-Fi for creating a sort of panic and intense debate around the uDAC 2, saying something like it was too expensive for the quality (the ODAC costs at least $50 more from JDS Labs, though technically it measures better) and I think he alluded that the DAC/amp uDAC2 combo could cause enough excursion to damage drivers... If you read his blog and the "engineer's note" on NuForce's uDAC2 page, it paints a picture where it's hard to tell if the "issues" are actually significant but that the debate was definitely ugly and full of insinuations. I don't really want to dredge that whole thing up, but I haven't seen discussion about the uDAC2 (or NuForce in general, but I don't look everywhere) for it's own merits by people familiar with the gear since that "scene," except here in the OP I see someone tested the original uDAC as working and I wondered if maybe someone has heard the newer uDAC2?
All that aside though, I've read many favorable impressions about the Modi, and the consensus seems to say the Modi is very clear and honest, generally a great value. I just am curious about the rest of the field too.