I signed up for an account on head-fi just to comment about the Xonar Essence STX. This sound card is AMAZING. The performance "out of the box" (default stock configuration in hardware and drivers) is better than any sound card I have ever heard or tested, and I have heard/tested about 20-30 of them now while looking for the perfect solution for my hi-fi HTPC setup. My goal was to go with a soundcard with balanced analog output (so I can remove any extra D/A-A/D conversion steps), so the Essence STX was the last card I tried due to its lack of balanced outputs.
I put the Essence STX in my HTPC, connected to a Crown XLS-402 amplifier via RCA-to-XLR cables (standard RCA "line" output on Essence), then to a few different pairs of speakers.
The first pair was my inherited set of mint Klipsch Belles (purchased brand new by my father in 1974 from Paul Klipsch himself). The sound was amazing. Crystal-clear, excellent separation and staging, extended rich and accurate bass, treble with amazing clarity and totally lacking in harshness, etc. It sounds so good that I just sat there and listened to about 10-20 albums in a row, I mean I wasted an entire day just listening to music (a very good sign when you've just purchased new gear). Turned the amp up until my decibel meter read 120db to see if I could hear distortion or if it would sound fatiguing, and then played a FLAC copy of the London Symphony playing the 1812 Overture with real cannon fire. It sounded awesome, with no distortion at all, and was surprisingly very easy to listen to.
Don't know what you guys are talking about when you say the JRC opamps lack bass extension. The cannon fire was powerful enough to knock dishes out of my cabinets, knocked a few pictures off the walls, and overall impressed the living hell out of me. Likewise, when the police arrived due to a noise complaint, one of the cops had his hand on his gun and said he had heard gunfire while approaching my house. I played the track for them and they got a big kick out of it and then asked me to turn it down.
Next was a pair of PSB Stratus Golds. Same experience. I noticed no weakness at all in the source, at any volume. The only thing I could comment on with the PSBs was that it sounded like the sound suffered a little bit of an excessive decay in the lower treble registers, and the upper midrange was a little boomy - but I believe that is due to the design of the PSBs, not the analog signal coming out of my sound card. The separation is phenomenal however, you can hear each instrument distinctly and clearly. It has amazing 3-dimensional staging, and the sound-stage is wide and deep, extending well past the side and rear walls of my listening room.
I can't say enough about this card. It is an amazing deal at $200. I have NEVER heard sound this good from my HTPC.
What's even crazier is that I'm now running unbalanced analog from the RCA output on the Essence to the XLR inputs on my Crown amp, and TOTALLY LOVING IT. I'm not going to change a thing. I never thought I would run unbalanced analog cables in my system again, after swapping to balanced a long time ago. But there is truly no distortion in the original signal, it's cleaner than the balanced XLRs I was running from the EMU 1212m.
To test this theory, I again plugged in the Belle Klipsch's and turned my amp all the way up and turned the PC audio all the way up, without playing anything. With the EMU 1212m, I can hear very quiet hissing and an extremely quiet hum with my ear pressed against the speakers (this is with the balanced analog cables). With the Xonar Essence STX, I hear nothing. Needless to say, it amazes me that I have less noise with unbalanced RCAs on the Essence than I did with balanced XLR on the EMU 1212m.
I know some people will say, well, balanced analog is going to be +4db, versus the -10db of the unbalanced. I have only one response to this. When you are pushing over 400 watts RMS to a speaker with 105db of sensitivity, you are going to hear EVERYTHING, regardless of whether your input is +4/-10db. Trust me.
I can't recommend this card enough. It's the best current hi-fi sound card on the market, hands-down, and I've tried everything: the Juli@, Emu 1212m, an offboard DAC1 (overpriced and overrated IMHO), the HT Omega Claro, Creative X-Fi, a few Auzentech cards, you name it. No other card has come close to the Essence STX in pure audio quality to this point.
