If there’s one part of the computing experience we’ve missed it’s something really high-end for audiophiles. And we are not talking about the dime-a-dozen 7.1-channel cards. Just looking at the STX you just get the feeling of quality. And it’s hard not to get impressed looking at it’s spec-sheet. The 124 dB SNR aside, the functional parts (opamps, DAC chip etc) are covered with an EMI shield. The Essence STX is built on a rather unusual four-layer PCB, ensuring excellent filtration of noise while the analogue output signal paths are also EMI shielded, ensuring that squeaky-clean signals are passed on. Additional power is required via a four-pin molex connector. This one is built on a PCIe x1 interface and ASUS has recently come out with a PCI version.

The DAC is a Burr-Brown (now Texas Instruments) PCM 1792A, considered an audiophile-grade component. beneath the EMI shield the opamps are mounted on sockets as opposed to being soldiered to the PCB. This allows swapping of opams to alter the sound signature according to taste. Note that the Essence STX is a stereo opamps on the card. Two opamps are the JRC 2114, considered good for audio applications. these serve as the current to voltage converters and are placed just after the DAC chip. They utilize the output of this chip and convert it, passing it on to the third opamp, the LM4562 which acts as the final buffer. Made by National Semiconductor, this opamp is quite famous and widely used by DIY audiophiles. Its claim to fame is excellent THD (Total Harmonic Distortion), quick slew rate and high bandwidth-all of these elements make for a superb choice for any discerning audience. Nichicon “fine gold” caps are used for all critical regions- a costly indulgence by ASUS and we highly approve.

Asus Xonar D2/PM

Now for the fun part – this sound card is the first one we’ve seen with an in-built headphone amplifier. This is good news for high-end headphone users, since headphone amps are very costly! The bundled software can switch between normal impedance,(up to 64 ohms), high impedance (60-300 ohms) and extra-high impedance (300-600 ohms), adding 0 db, 12 db and 18 db (respectively) to the gain to match headphones of varying impedances. The Essence STX has a pair of RCA outs for stereo, one 6.3 mm headphone jack, one 6.3 mm analogue input jack and digital-out supporting both coaxial and optical  connectivity on a single jack.

We tested the Essence STX with some stereo speakers first – our Genelec 6010A active loudspeakers with the 5040A active sub-woofer and some SACD .FLAC rips. The imaging (sound standing) is spot on. The bass, while ample, is not excessive and won’t intrude on the mid-range. But it goes low down and does so cleanly and with nary a hint of loss of control. The mid-range is liquid and wide with lots of detail to be plucked from between notes. Male and female vocals alike sound rich and lush without being overly warm. The highs are incredibly detailed and transparent. We felt the highs were slightly over emphasized, but not in ordinate. Quite the contrary, this is just the tool for discerning listening sessions; particularly pieces with instruments have great rendition. Next we plugged in some quality cans and we’re pleased to report the STX handles itself admirably – the sound is clean, without any sort of noise and very musical-the word balanced came to mind as the incredibly detailed Grado SR225 seemed to get a bit of needed bottom end grunt from the headphone amp unit. What is equally hard to miss is the immediacy  of the detail, there is no unnecessary delay to notes,attacks, decay, instrument  reverb-everything is spot on and tonally accurate. The Essence STX will also drive something as beefy as the Sennheiser HD 650 quite well, but not to the same level of analytical detail as a high-powered headphone amp.

Wealso tried the STX with games and movies, although not its forte, it handles games quite and with very accurate imaging-something necessary for a proper gaming experience. Movies are fun too, with action scenes getting their just rewards – the Essence STX never loses control and detail  and its surround imaging is superb, despite the lack of additional channels.

So ASUS finally delivers something “Stereophiles” (including some of us) around the world have waited for. So what’s the trade off ? Well, it won’t replace that Zana Deluxe Headamp you paid half a year’s salary for and some purists will sneer with contempt at people who use their PC for music. Moreover it isn’t cheap, at $249, but then quite frankly neither is a ticket to a Pink Floyd concert. We feel it is well worth the price with its premium quality innards and audio performance. It serves a niche segment and does so exceedingly well, therefore those on the lookout for something similar won’t flinch one bit.

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