Pros: Excellent shielding, upgradeable op amps
Cons: Drivers brickwalled by MS-Windows 6+ audio stack up to now
I originally purchased this audio card for an Asus® CM1630-06 previously upgraded with the same vendor's EAH6850DC/2DIS/1GD5 PCI-Express x16 video card plus an Antec® TruePower™ 750 Blue for sufficient video performance for podcasts and similar live over-the-Web activities at UStream® Television. Even with the bone-stock JRC2114D dual operational amplifiers in the I-V and National Semiconductor®/Texas Instruments® LM4562N in the line-level buffer position, this card is plenty accurate and has room for further tuning. I found that the Essence™ has one of the lowest noise floors of any card on the market, almost certainly due to its conservative, radio-grade shielding approach; the EAH6850DC in the next slot (literally) added negligible noise. The main outputs are two RCA jacks (2 Speakers) and one 1/4" (6.3mm) jack (Headphone); the internal headphone amplifier, a Texas Instruments® TPA6120A2 dual power amp, has three gain settings for different headphone impedances and sensitivities. The on-board digital-audio output, which can handle RCA coaxial and 3.5mm optical, can transmit PCM or Dolby® Digital Live to an external DAC, receiver, &c. The Unified XONAR® Software by Brainbit, Release 1.53 (C-Media CMI-8788 Driver 188.8.131.525), runs stably on most Windows boxes.
The one downside I encountered is apparently due to a core software issue inside Microsoft® Windows® 6.1 and 7.0 with Service Pack 1, viz., an issue with the resampling DLL in the audio stack that affects other audio chips besides the AV-100 and related C-Media® chipsets (see "Xonar Essense stx Random LOUD high pitched Ringing Noise?"); an updated set of Audio Drivers C:\Windows\Sys*\WDMAud.drv has been released as part of a hotfix for Windows® Se7en™ 7.0.8001 and Windows® Server 2008 Release 2 6.1.7601. (This was a fail for addressing the 6 kHz scream problem, see Thread cited.)
Update: Due to the 6 kHz scream rearing its ugly head again, I transferred the STX to the Hot Rod gPC™, and it is happier than a hog in slop under ubuntu® 16.04.1-LTS. The Advanced LinUX Sound Architecture Project has an optimized driver in snd-virtuoso; ALSA Mixer can access not only gains for Mic/Line In and Aux In, but also Record Ons as well as Monitor Mutes for Mic/Lin In, S/P-DIF In, and Aux In - a software counterpart of a full-on recording console. C-Media® CMI-8788 Driver 184.108.40.2065 (included in MaxedTech® UNi™ XONAR® Audio Software™ 1.81a Rev. 2), a long time coming to Microsoft® Windows® 10 Build 1607 10.0.14393.576 and later, is a fix committed for the 6 kHz scream that defied ASUSTeK's engineers for nigh onto a decade, but it has the same restrictions as earlier versions in terms of controls.