I know I'm replying to a fairly old comment, but - I'm the guy who made the Bioshock Infinite virtual surround comparison video. I've been long planning a much more comprehensive comparison that would include SBX, as well as several other virtual surround technologies I was able to get my hands on (though I'm still missing quite a few, but it's unlikely I will be able to get the necessary hardware in the forseeable future), but still couldn't get to actually do it - amongst other reasons because I'd like it to be as complete as possible, covering as many of the available virtual surround solutions as possible, including different settings and modes. And that's not an easy thing to do, and, worse of all, a pretty expensive thing to do.
However, I can tell you absolutely certainly, that as far as THX TruStudio Surround on the Titanium HD and SBX Surround on SB Omni 5.1 are concerned, they definitely sound different (even through the same DAC). I haven't had a chance to compare SBX Surround on different hardware to confirm the way it sounds is independent on hardware, but on those two devices, there's definitely difference. THX (to me) sounds more "studio-like", with less reverb and affecting the original sound less, while SBX sounds a bit more "cinema-like". I also hear difference in positioning of the virtual channels and in how the slider affects the overall sound - THX (again, to me - YMMV) sounds a bit more "spherical" if you will, while SBX kinda sounds "stretched to the sides" a lot, there's a more emphasis on the left/right positioning while the front/back is deemphasized even further than it is with THX.
If I set the surround slider in THX at around 20 percent, I can get a sound that kinda sorta surrounds me, even though I'd like the rear cues to be more prominently placed in the back and less to the sides. With SBX, I pretty much can't find a setting I'd like - for me, it's either the front left and right channels sound way too separated for my tastes while the rear left and right cues are at least somewhat coming from the rear, or I can tweak the settings to make the front cues sound more natural, but then I'm pretty much not able to tell side left/right cues from rear left/right one's - they just sound like they're both coming from almost the same direction respectively, too much to the sides.
So as you can probably tell, I'm not overly thrilled by SBX. I still prefer THX Surround over the SBX one, and I much prefer Dolby Headphone over both of them, despite its reverb (which you can get used to, kinda) - not just because thanks to the virtual speaker shifter, I can position the virtual speakers EXACTLY where I want them, tweaking the surround experience precisely to my needs.