a USB audio card is nothing but a dumb finger sized processor that does all the audio processing on it. In fact the built-in soud card is far superior in terms of quality compared to that X-fi.
2| the x-fi badge is a tag once used by all the big names in the IT industry now its a shell of its former self and creative is doing nothing to improve that image. The best bet you have now
of getting a quality piece of hardware with the x-fi badge and good
support from creative is the titanium HD but thas for a desktop not a laptop.
3| creative can't do true positional audio ita all audio/software emulation so its not really what you're looking for.
4| did you think about hooking up the audio device to a speaker system or a pair of headphones?
5| if its speakers, you should go with the onboard device.
6| if its headphones that is causing you to get an add on USB card, then forget about the card...and look into a pair of tritton ax720 pro's or AX720's if you have more dough then you should chekc out astro gamers headphones with a mix amp that can accept 5.1 audio via optical jack.
hope these help
BTW welcome tot eh forums, newcomer!