Pros: Excellent shielding, upgradeable op amps
Cons: Drivers brickwalled by MS-Windows 6.1/7.0 audio stack
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 additional 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® TP6120A2 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 126.96.36.1995), runs stably on most Windows boxes; I have yet to test the Virtuoso driver from the Advanced LinUX Sound Architecture Project (LinUX Kernels 3.0-up) with either the Essence™ ST or STX.
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. As of 26 January 2013 I do not know whether this issue has been resolved for Windows® 8.0.10000 and Windows Server 2012 8.0.10000 (MultiProcessor Kernel 6.2.9200).
Users in need of an XLR-ready audio card who have relatively RF-quiet systems may be better served by the Auzentech® X-Meridian® 7.1 2G (C-Media® CMI8788) or X-Fi® Home Theater HD™ (Creative® CA20K2), both of which use an Auzentech-exclusive microphone preamplifier to take input from balanced dynamic microphones widely used for recording studios and live sound.