People have tried to use computers as console surround processors before, and nobody's found a good, low-latency solution yet.
Honestly, you're better off just plunking down the cash for a Mixamp.
It's because Creative's software OpenAL renderer that they use for "fake" X-Fi devices (basically all the USB ones and the XtremeAudio cards), along with all SoundCore3D devices (Z-series cards included), has flaws compared to the hardware OpenAL renderer used in the true X-Fi cards.
It was flawed enough to utterly refuse to let Thief 1/2 enable DirectSound3D hardware acceleration even with ALchemy set up properly, though they thankfully have native OpenAL support now. Battlefield 2 also sounds noticeably off if you try to max out the audio quality, X-Fi mode and everything, on an audio device that isn't a true X-Fi card with the EMU20k1/20k2. It lets you enable it without throwing out errors, but you notice that there's reverb on the menu sound effects that shouldn't be there, among other things.
This isn't something you'd notice with more recent games that do all their mixing in software, of course.
Also, there's a second matter with the Sound Core3D devices that I don't like as much, and it's THX TruStudio Surround. I think it just doesn't sound nearly as good for positional audio as CMSS-3D Headphone does, be it from the Titanium HD in Entertainment Mode or the Recon3D USB, even for games with software-mixed audio. Of course, that's just me and my ears speaking, and your experience may be different.
The first thing I'd check is the mixer. You have to mute the microphone under the "Playback" section of the mixer, while leaving it unmuted for the "Recording" section.
The mic input on my Titanium HD works without issue, other than that it lacks a mic boost and thus should be used with more sensitive microphones.
