Hi, everyone. Rory here.
I didn't expect this thread to grow so rapidly, so I'll try to address everything in sequence.
When performing the game testing, I simply ran each sound card's output in 2-channel mode. I didn't test the combination of Dolby Headphone and EAX, but the suggestion has me curious now. I'll give it a go, and report back. My headphones have good enough stereo imaging on their own that they were able to place sounds to either side of, or even behind my head, so I don't think the fact that I used headphones in testing was detrimental to the goal of the review -- to ascertain any difference between the environmental effects added by either sound card.
Vista testing was also scrapped for a similar reason -- I didn't want to add unnecessary variables in the testing (compatibility with ALchemy, for example, or half-baked Vista drivers) that might skew the results in a particular situation, but don't provide a true picture of how the two processing methods compare when everything is working properly. The goal here wasn't to compare the ASUS product to the Creative product as a complete package, but to compare Creative's EAX 5.0 effects to ASUS' DS3D GX effects in terms of quality and game experience. I did try to install and run both cards under Vista with mixed success, but if your games don't use OpenAL and aren't compatible with ALchemy, then you'll be out of luck when it comes to 3D hardware-accelerated effects on the Creative card. In this case, it seems that ASUS' solution is significantly more attractive -- it works with both DirectSound3D and OpenAL games without a translator like ALchemy.
FPS numbers, in retrospect, might have been nice to include in the comparison. However, I wanted to focus my efforts on the experience contributed by the 3D audio engine itself, which seemed to be the main point of contention between ASUS and Creative. Creative alleged that the difference between EAX 5.0 and DS3D GX 2.0 would be audible -- and not limited to the (fairly inconsequential, in my view) performance hit that comes from software-based DSP processing.
The X-Fi 24-Bit Crystallizer was not enabled when testing with the Creative X-Fi card. Again, this was done to eliminate unnecessary variables that could affect the conclusion.
In the earlier Xonar D2 review, an Audigy 4 card was used instead of an X-Fi card because I couldn't beg, borrow, or steal one to use in the comparison. If I could have, I would. However, the Audigy 4 card still offers hardware DSP processing of EAX 1.0 and 2.0, which are the only EAX specifications tested by RightMark 3D Sound.
I hope that answers everything that's been asked so far. Keep the questions coming -- I'm loving the interest that people are showing in this subject.