The D2X' audio quality is superb, I use it in combination with a 5.1 surround receiver connected by Optical SPDIF and the end result is astounding.
Music, Films and Games are all crystal clear, with an audible difference in quality compared to my previous on-board audio solution.
The only downside this has in my opinion is that you'll want to rip your entire CD collection to your computer again, if only to store them as a lossless format because the difference in quality between standard 128 kbit audio and lossless is clearly audible with this card thanks to the very high quality hardware used.
It has EAX support for older games but it really shines under Windows Vista or Windows 7 where EAX and Creative hardware audio no longer function properly.
Not messing around with the limited game support that ALchemy provides, ASUS uses DirectSound3D GX which will work on any game that uses DirectX for it's audio. For newer games it uses standard DirectSound3D and OpenAL.
The card has the ability to convert any audio output from your PC into Dolby Digital or DTS which makes connecting this card to a receiver through it's digital connection a great option, providing either All Channel Stereo when no surround information is available or up to 7.1 surround when it is.