You didn't mention what you're plugging your computer audio into. For example if you're using headphones, then the headphone impedance and the card's ability to drive it are going to vary wildly depending on the specific amplifier circuitry involved. If you're connecting a line level signal to an external amplifier this is not so relevant, although there will be some line-drive circuitry on the board or in the chip, and this will vary, and can make a (marginal) difference if you have long cables.