S-LOGIC isn't in the same genre of "stuff" as Dolby Headphone. It's...different.
Look at how the drivers are placed on a "normal" headphone, let's pick on the Sony MDR-F1 as an example (thanks to whoever took this pic - the F1 angles its drivers for improved imaging, but that's become increasingly common since it's release some 12 years ago):
And then how they're placed on an Ultrasone with S-LOGIC (thanks to whoever took this pic - the driver is the "mouth" (it looks like a smiley face; it's actually oddly centered in this image - the proper orientation is with the left black dot at top (if you look closely you'll see the gimbal in the background, and it'll make sense)):
Here's another shot:
That off-centered placement influences the soundstaging and presentation, and the entire thing (both the placement and the result) is what Ultrasone calls S-LOGIC. It's never "off" because it's just a function of the design of the headphones. You can enable any up-stream processing you'd like, and it's really up to your own preference. It isn't the same thing as "5.1 headphones" or anything of the sort (although Koenig did propose a four-driver version, which I've never seen implemented). The sound-staging on an Ultrasone is good, if S-LOGIC works for your ear shape (which is not universally guaranteed), but there are other good choices as well. For example the F1's used as an example above (clever, aren't I?), and many Audio-Technica designs that also rely on angled drivers. Personally I've been impressed with Ultrasone and gaming, but of course YMMV. I have found that after a relatively low price/quality "break" the improvements in performance, at least for gaming, are minimal (in other words, while I feel that something like the HFI-2400 is a dramatic and huge step-up over cheap headphones or bad speakers, I don't feel that my electrostats are a dramatic and huge step-up over the HFI-2400 within the context of gaming). Finally, I will add that headphones with lots of/good bass response make gaming a lot more fun imho - the HFI-2400 are a good candidate all around based on that (assuming S-LOGIC jives with you).
You can dig up Koenig's papers on S-LOGIC for more, including his study of user preference (a word of warning: afaik he only writes in German, and the papers are (oddly/poorly) translated to English for publication; they can be somewhat kludgy to get through).
