I have been having a conversation with an embedded software engineer (the types that make things like DACs professionally) and some recording engineers. Here is what I learned so far. I will update this as my conversation develops. (The long version is followed by the short version).
The long story:
There is USB class 1 and class 2 implementations. Class 1 requires no special device driver. Class 2 does require its own driver, but it is a more accurate way of transferring information using USB. In other words, there is much less jitter (distortion) with class 2 devices. And custom drivers for this are only available for the Mac and Linux. As a consequence, very few DACs support class 2 designs. The ODAC is class 1 design that uses one of the few chips that support 24-bit data.
All PCM/SPDIF/I2S DACs have the most accurate timing by the nature of the chips used in their design. Next are class 2 designs. Next are USB class 1 designs operating in isochronous mode, which is the case with the ODAC. Then finally there are older USB designs which are, according to one engineer, "crap".
All DACs that are designed to faithfully reproduce the audio signal will sound the same. But some DACs introduce a type of distortion that makes the music more pleasant to the ear. This is where they can differ in how they sound. Please note that the latter DACs do not reproduce the sound accurately on purpose. For instance, this is the reason why there are those of use who like tube amps. Tube amps generate distortion by introducing the pleasing even harmonics to the sound. I also think this is how DAC manufactures can differentiate their DAC from other DACs.
In recording studios, the difference between a budget properly designed DAC (to the numbers like THD, SNR, FR) and high-end DACs (like the Benchmark DAC) is noticeable but not anywhere near as great as the difference between a good budget DAC and a poorly implemented one. We are talking the difference between inches compared to feet here. IMO I think the ODAC fits in the category of a good budget DAC.
The short version: The difference is in older poorly implemented USB and those of current day USB. For current day USB chip implementations, they are all the same.
Am I verbose or what??
PS: I will ask about the differences between asynchronous compared to isochronous implementations of USB.
EDIT: Class 2 USB is not natively supported in Windows. But this person said it may be in Mac OS and Linux. I just checked and they both do.
Edited by r010159 - 4/15/14 at 2:16pm