I'm also using the latest drivers, and firmware, from Creative. Still, could you try plugging the headphone port? It may do nothing for you, but I'm interested if doing that does make such a large change that I experienced so I can find out if I should return my Omni for a replacement. Then you can tell me to stuff it
My Denon 4520CI has DTS Neo: X and Audyssey DSX. If you're not familliar with them, Neo: X has a more centered listening point while DSX is slightly back so there is more emphasis on front sounds than rear.
I prefer Neo: X over DSX for my real speakers for gaming, it keeps sounds the same "distance" as the sound pans from speaker to speaker when turning around. 9.2 setup with Wides ATM, so I would be extracting embedded sound queues either way but both do it differently.
I bring this up as this is my current opinion from results I hear with my Omni. SBX + headphone port plugged with DDL disabled produces something thats more similar to DSX, whereas SBX + headphone port plugged with DDL enabled gives me something more similar to Neo: X
Both results are good, one focuses on even distribution of sound all around you and the other emphasizes the frontal sounds more. Please note that I say similar, this is not literal and only used to illustrate the general relativity of their differences. I won't say which I think is which, try it out for yourself. I don't want to risk influencing someone's decision by giving specific expectations
Of course it is as you say, you can only make use of this option if you can decode said DDL signal.
I've been using the RAW track in
THIS THREAD for testing. The first 40 or so seconds is the ingame speaker test, followed by three segments of the intro that is great to test audio localization. I really like this because there is no video for you to rely on for location. I'm not trying to say X setup is wrong, only that it's worth trying with and without DDL encoding (Windows@ 5.1, Omni set to "Headphone", SPDIF cloning)