Not sure the quality of that M-Audio card, but I think most say to go with an interface simply because they tend to be higher quality than consumer soundcards. If the card was designed by a company that pretty much solely deals in recording equipment on at least the pro-sumer level, you should be fine.
Otherwise the advantage I see is that USB is an easy addition to the system, and is easily portable to other machines. Plus, you can use em on laptops. And yeah, since they are external, they can grow much larger than a PCI card can, so there is another advantage.
All I can think of at the moment, but I hope that helps.
