While I was doing my research I came up on a direct comparison between Asus Xonar U7 and Creative X-FI. I can't seem to find it now, though I remember that the reviewer was slightly inclined towards U7.
What I can say is that, apart for the few problems I had with the U7's line-in (which I solved acceptably - see my previous few posts in this thread), it's an excellent buy for me.
Consider that it's my first external sound device, though. I only had integrated sound cards.
Last night I bought a phone jack-to-RCA adapter, to plug my desktop speakers in the U7. I have my headphones plugged in at all times, and the switch from one to the other goes well. There's around half of second of silence between redirecting the sound to the other output, but it's not a problem.