I might recommend something like this...
http://www.circuitcity.com/ssm/Onkyo-Home-Theater-System-HT-S590S/sem/rpsm/oid/148410/catOid/-12954/rpem/ccd/productDetail.do
The Onkyo surround setup gives you a full 5.1 standardized system. It's a great price (under $250) and allows you a true audio/video upgrade path that is consistent with industry standards. Unlike a PC speaker setup which is locked in and tends to not have anywhere near the flexibility of a A/V system, this one will give you some room to grow. Some serious room!
How does it work with your PC? Well, set up the 5.1 system how you want it in the room. Then, take the digital output from your sound card and run it into the receiver. That should be it. The X-Fi appears to have a 3 in 1 jack that includes digital audio, and you should be able to run that straight into the receiver.
To use it: Set your receiver so it is looking at the input from your computer. Now, just turn on your computer. That should be it. In the future, when you turn on your computer, turn on the receiver and that'll do it - nothing else to setup or configure.
Best part? Moving forward, you can move this system to any television you want - like a 42" plasma or LCD. You can hook up a DVD player, cable box, VCR, etc. and it has some room to grow. If you aren't happy with the way the subwoofer sounds, you can hook up a different subwoofer, or two, if you want to (and can afford it). Unlike PC speaker setups - you aren't locked in.