Any of you tried Razer Surround? I've given it a go after years using Dolby Headphone on my Xonar STX and for me its miles better for positioning. Slight deterioration in quality but nothing significant for gaming. DH does a good job of simulating a 5.1 speaker system in a room, but that's the problem - you are always stuck in a room with 5 speakers around you, which is weird when playing something like BF4. RS sounds more natural and clear to me. Had a big grin on my face when I first tried it out - even just being able to position where your squad mates are when you running to an objective is so much easier.
Everyone's different when it comes to HRTFs, but that's one advantage of RS - there is a degree of tuning possible. Just started to play with the TB Isone VST - routing my GPMAA streaming into it. It's very tunable. I'll see if I can get a good virtualisation of a studio monitor setup without molesting the overall sound; I've heard it can be pretty good when tuned. DH was good at getting the sound 'out-of-head' but just messed with the overall tone and balance too much.
Another advantage of RS is it's not tied to hardware, so I can run it with my ODAC + O2 amp. Got no more reason to use my STX.
Never tried CMSS or the others. Heard pre-Vista CMSS + EAX was pretty good. What happened to AMD TrueAudio? Anyone tired it out? To bad Creative murdered A3D... Pretty sad that we're still stuck with just virtualising in 2D, and very poor environmental simulation. Hopefully all the VR stuff will lead to a bit of progress.
(if you are trying out RS, you should turn of 'bass boost' and 'stereo enhancement' which I think are stupidly enabled by default. As well as the other rubbish on that page. I think they might even be enabled in the demo version, which you can't customise I just bought it because having a soundcard agnostic solution sounded really good)