I originally purchased the HS-1A when I was still on Bethel Island in East Contra Costa, CA, USA, as a test item; 50mm transducers were an up-and-coming item at the time.  Sound proved a little better than the Plantronics® GAMECOM® 380 that would supersede them.  The sound went bad, however, after only three months; when I opened the right earcup to investigate, I found much to my shock that all conductors in the harness are at best 30 AWG.  Needless to say, repair was impossible with the tools I had at the time, and the earcup's lack of available space precluded the major cable upgrade necessary to return the HS-1A to service.  Disposition:  Scrapped.
 
As of 21 August 2016 I am still on the hunt for a headset for the ASUS® XONAR® STX, and the HS-1A is clearly a did-not-start; although some might recommend one of the Sennheiser® PC-Series gaming headsets, my cable construction requirements are not currently satisfied by any computer manufacturer and I may end up getting a Heil Sound™ Pro Set™ Media Pro™ despite questions about the earphone response, as it is one of the few computer headsets that ship with a full-on radio-grade harness (4 x 20 AWG-cored coaxial cables) with dual 3.5mm TRS plugs.

I purchased this card originally to replace a failing Creative Laboratories® SB0350 PCI 2.2 audio card (Creative Technology CA0102 DSP) and SB0250 I/O Drive in the Hot Rod gPC™; but it was quickly transferred from the Hot Rod to my ASUS® CM1630-06 as previously upgraded (Advanced Micro Devices® Athlon II® X2 220, RS760G/SB700 chipset, PCIe RV970 Pro GPU (aboard ASUS® EAH6850DC/2DIS/1GD5); 750W Antec® PSU) when the 6 kHz scream that randomly dogged the XONARESSENCESTX/A - which ASUSTeK engineers were never able to replicate on a consistent basis - reared its ugly head again in Microsoft® Windows® 6-up (see "Xonar Essense stx Random LOUD high pitched Ringing Noise?"). I anticipated severe digital-noise issues due to the proximity of the EAH6850DC (forced by the design of the CM1630's M4A78LT-M 'board), but these proved little worse than the XONAR's; the rear audio proved clear enough for my requirements and the front audio proved, much to my surprise, less noisy than the XONAR's. (The XONAR ended up in the Hot Rod and runs even happier on the ALSA snd-virtuoso driver in LinUX 4.4 than on the C-Media® driver in the MaxedTech® UNi XONAR Audio Software 1.82 in Windows 7.0.8001; ALSA can access and mix all inputs on the XONAR.)

The Creative Technology CA10300-IAT DSP on this card (joined to the host system with a PLX® PCIe-PCI bridge) is a product improvement of the CA0108 last used in the SB0400 Audigy2 Value and is specified for 106 dB signal/noise. This card packs an integrated headphone amplifier (unknown make and part number, rated for a 600 Ω max load) for the Front Panel header, which had no trouble at all driving my Plantronics® GAMECOM® 380 headset. In addition to two mic and one line ins, all unbalanced stereo with +3.6V for the mics, at the rear panel, the SB1550 has a clean enough Front Mic input for typical computer users on its Intel® HDA-compatible front-panel-audio header (9 of 10 pins, Pin 8 key). Analog outputs at the rear panel are Front L+R, Back L+R plus Side R, and Center + Subwoofer + Side L; a TOSLink optical send is provided for Digital Out. Creative Laboratories has full driver and application support for Windows 10.0.1nnnnn as of August 2016 for this card; initial tests of the integrated synthesizer with Cakewalk Music Creator 5.0 (a carryover from Win 7 through the dist-upgrade) under Win 10 Version 1607 10.0.14393.51 performed within spitting distance of the simulation. (The SB1550 had problems in LinUX Kernel 4.4 with an ALSA snd-emu10k1 driver originally intended for the EMU10K1, EMU10K2, CA0100 and CA0102, as the CA10300-IAT has some behavioral differences from the CA0102 at the control level; those problems don't exist with the correct Creative driver/app suite under Win 10.)

This card having no Digital In, those needing a card with a Digital In with behavior consistent with the SB1550 may be best served by the E-MU®/Creative Professional EM8984 0404e or packages based on the EM8986 1010e (both, sadly, also discontinued). The SB1270 X-Fi Titanium HD, which packs a CA20K2 DSP, is unusable in LinUX, the Advanced LinUX Sound Architecture Project having abandoned work on snd-ctxfi; and the Recon3D and Z/Zx/ZxR family are only partially supported in ALSA. Also, for a successor model to the SB1550, I have to require both shielding consistent with the SB1270 and SB1510, and re-adding a TOSlink Input for S/PDIF Audio.

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 Japan Radio Corporation 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 four 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 7.12.8.1795), 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® 16.04.6-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/Line In, S/P-DIF In, and Aux In - a software counterpart of a full-on recording console. C-Media® CMI-8788 Driver 8.3.1.1825 (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.