Same here. Before I really got into PC gaming I used the Astro Mixamp on Xbox 360 (mostly for COD), and always felt I had an edge when it came to positional cues. When I built my PC I went with a Xonar DGX, and was extremely happy with it. I always like trying new things though, so I replaced the DGX with an X-Fi Titanium HD/Magni/K7XX. Since then I've never really been completely satisfied with the CMSS-3D in comparison. My friend is sending me my old DGX this week, so I will be able to test the both back to back. When I still had the DGX I was using a pair of Razer Orcas/Steel Series Siberias with a custom mod mic. I'm curious to see how it sounds with the K7XX, but I'm thinking I might get some feedback without a proper DAC like you mentioned in your experience. We will see.
With the release of Modern Warfare Remastered last weekend I decided to try out my K7XX for console gaming, and I switched back and forth between them an my HyperX Clouds. I also went back and forth between my DSS2 and Creative Extigy. Both were being double amped through my O2. For a closed back "gaming" headset the HyperX clouds do alright, but it's immediately apparent how much bigger the sound stage is with the K7XX. After switching back and forth between the two I decided to just use the K7XX. I felt like the DSS2 had better positional cues once I got the EQ and surround angles set correctly, but I was only getting chat out of one ear, and if I set chat to come out of speakers throguh the Xbox settings it was extremely loud, and there's no way to turn voice chat down without turning down game volume as well. This was annoying so I switched back to the Extigy. Overall the CMSS on the Extigy sounds better, but I don't think it performs better. I was constantly getting shot in the back, and not being able to tell direction of gunshots/footsteps. It was almost like the sound stage was too large. Gun shots are almost soft, and hard to tell the direction they're coming from. So, in short, I think the Extigy has better sound, but not better positional cues and accuracy in comparison to the DSS2. I ordered an Astro Mixamp Pro 2013 edition over the weekend, which should be here in the next day or so. I'll test that out along with the DGX on PC and make a conclusion. Still think I'll pick up an X7 to test so I can cover all my bases.
On the 6XX..I didn't even want them for gaming sine there are better options out there, but it would have been nice for listening to music. I guess it saves me $200..for now.