I'm upgrading my sound card soon. I am using a Recon3D right now, mainly because I got it on clearance for $5! But I want to upgrade to something a little more versatile.
I'll be getting the Sound Blaster Z, which is basically the same thing as the Omni except it's a card, not a USB device. This gives me a nice 600ohm amplified headphone jack, as well as an optical out. Later, I can use the optical out to pass processed virtual surround (stereo sound) to a DAC/Amp combo if I want to upgrade the sound. I'm mostly buying the card for the DSP (virtual surround).
I believe the Omni can be used in the same way. My understanding of the difference between the internal one and the USB one is that the USB one uses more system resources. If you have a halfway decent system (which I assume you do if you're gaming) you probably won't notice the difference.
I think the Omni is a smoking deal. It's like $60 (correction, price went up in the last two days, it's $70 now) on Amazon. It's not the best sound card you can get, by any means, but it's a solid choice and it allows you to upgrade to a real DAC/Amp easily later if you want to throw more money at the hobby.
BTW, the X1's are supposed to be pretty easy to drive. The Omni should have no problem with it.