I have no idea why I'm asking this question, as I sort of know the answer. Although your SB omni outputs 600 ohms... @_@
I'm guessing these values are just marketting tactics?
Just wanted to chime in on this, ohms are only part of the amping equation, and the way soundcard manufacturers use it amounts to "just marketing fluff."
To make an analogy, it's like trying to figure out speed just from knowing the distance travelled...without knowing how much time it took.