Razor surround 7.1 software and Creative’s MB3 software bundle with SBX appear to be the 2 major software solutions for the most accurate positional audio when using onboard hardware and stereo headphones.
Does anyone here use either and which do you think has better positional accuracy?
Neither 
Creative’s CMSS-3D, IMHO, was the best. But they phased it out for SBX for some odd reason. SBX is pretty good though, but not quite as good as their older tech.
HEre’s a youtube video that might help you decide what you might personally prefer:
Make sure you disable any virtual surround sound tech you currently have in order to get only what the video provides.
I like that the Razer one is configurable, however I don’t think the sound stage is “wide” enough, or the effect pronounced enough to make with worthwhile over SBX - which is what I use on a pair of Sennheiser cans.
Dolby on the other hand I prefer for movies. Gives a more bassy result, but it alters the sound too much for gaming purposes, IMHO.
But CMSS isn’t an option. I had a titanium Fatality card years ago with that but that’s outdated stuff now. The problem with that video comparison besides the fact that each comparison is way too long is that it’s hard to listen for exact positioning between each one, they should have done a different game where they play the exact same scene for each one so it’s more like a side by side thing.
So basically all I can tell from that video is that SBX sounds louder with raised EQ in upper frequencies. Razor sounds flatter and Dolby sounds rather nulled like the volume is turned down a bit. Didn’t help me decide which had better positioning but maybe they are both similar enough that it doesn’t matter.