USB/external audio devices can be pretty phenomenal, and easily switched across machines. There are minor additional signal latencies, but not enough to matter for lowly HD audio output unless the USB controller is severely overcrowded. Many motherboards have weak or problematic USB power management, regardless of specs, which might be problematic when USB devices are being hotplugged or charged or whatever (often a sporadic issue easily fixed, at least for a while, by just restarting the system). But the main disadvantage of USB audio devices is simply cost, PCI/PCIe sound cards generally cost much less. Better motherboards tend to add components which emphasize audio, and gamer/enthusiast motherboards tend to sound remarkably decent - as good or better than any low-/mid-priced audio card - if you have such a mobo then you can't actually upgrade sound quality without a buying high-end (and high-priced) audio device.
"All opinions are not equal. Some are a very great deal more robust, sophisticated and well supported in logic and argument than others." - Douglas Adams
[/Korth]
