I just got a Xonar Essence STX to replace my Xonar D2X. Let just say that when i got my D2X it was such great departure for me sound wise in that i became more concerned with the quality of sound and started looking at certain features that would grant me that. Before that i used an external DAC in the form of a Phillips 1505U dolby headphone receiver (which i still use for my PS2, PS3 and 360 for multi-channel gaming) which got me to really appreciate headphone DSP tricks especially with movies.
With the Xonar D2X i got first hand experience with lossless audio and a superior DAC and my ears were blown away. Granted due to its nature the most i could ever experience was 16 bit 48khz audio on my bluray movies (though by using AnyDVD HD and Media Player Classic that was void) it still sounded a hell of a lot better that the lossy dolby digital and DTS audio tracks (even the awesome sounding 24 bit DTS core tracks on mkv files). Coupled with the dolby headphone DSP technology i have never experienced sound with such clarity in my whole audio listening life. I have had countless high-end creative cards at the time and nothing has matched the Xonar, not even the Auzentech Prelude CMSS-3D matched it in movie quality.
I never thought i could experience better audio than the D2X until i listened to the STX. My 24 bit 96khz audio tracks sound amazing, my blurays sound amazing - i slapped in Transformers and was blown to the next universe - and because of this i don't think i can ever experience anything less.
I recommend the Xonar D2X, quality like that is unbelievable but the Essence STX in a different universe. Expensive yes but coupled with a high-end headphone (Checkout my sig) it will be like someone pouring honey into your ears
Fantastic. Well done Asus