External Sound Cards

Now that I have purchased a new headset (Senn 350s), any of you use or used an external sound card?  If so, what are some recommendations?

I was looking at creatives X-fi surround 5.1 or their X-fi Go! as possible choices.  I know steelseries makes one.  Overall, the idea is that I'd like to take advantage of my new headset, but not drop a lot on a soundcard because later when i buy a new build, I was looking at having DS fix me up with an internal sound card.

Overall I am not looking to debate sound cards and all that, I just was wondering how these external types seem to pan out.  I believe my momma board is a p5W dh deluxe, or close to that name, and I get fairly decent sound now from the onboard.  So I may just hold off and use that until I purchase a new PC.

With the snow coming tonight, I have a while to play around with and see what the on board sound will do with the Senns, and then I would look into external sound cards.  But for now, any info you all have may help me and would be appreciated.  I'll add the info to the review data I have checked out so far.

Thanks