Software

The driver has the same features as on the original STX. There are no big additions except for, perhaps, low-gain mode, which suits IEMs that are not super-efficient. The STX II driver suite features the usual modes. These span from gaming to music production and HiFi. Usually, only one setting will set a mode apart, but they are quite handy if you want a different setup for games, movies, and music.



All the usual add-ons are available in the bottom panel of the driver. You get Vocal-Fx and, of course, a nice parametric equalizer. People who want a sound card for occasional recording could be well-served by the STX II as there is full ASIO support as well, which is great.

Performance

ASUS created a good card with the STX and the STX II is even better. While technical aspects have been upgraded, the audible difference is small, and you need a hefty set of headphones to be able to tell as lower-end headphones will mask the differences. There seem to be some noticeable changes in the treble area with better headphones and headsets, like the HiFiMAN HE-400/500/560, QPAD QH-90, or KRK KNS-8400, but the changes are minute. Soundstage-wise, the new STX II does a slightly better job across the entire range as there is a gain in the quality of the timbre of instruments and the tautness of the bass with über-high-end headphones. The slightly better timbre is welcome as is it on par with the similarly priced JDSLabs O2+ODAC and its newer distant cousin, the C5D, both top-of-the-line amplifier and DAC combos which are less versatile than the STX II.

The card comes with the Muses 8920 op-amps pre-installed, and they do sound great. They are similar to my AD817BRZs in sound as they seem slightly warmer than the LME49720, which you also get with your STX II. Picking between the LME49720 and Muses 8920 is difficult, and the differences are minute on even ultra-high-end gear. I think the LME49720s pairs a bit better with the revision one HE-560s we have had the pleasure of testing, but, again, your mileage will vary. I think it is great of ASUS to supply you with two brilliant choices since sourcing these op-amps from vendors three at a time is extremely expensive, and you would run the risk of getting counterfeit parts over Ebay.

Giving you a much larger usable range with both efficient full-sized headphones and in-ears—both could pose a problem with the original STX—the STX II's low-gain setting is actually much more useful than the one on the STX. The gain is still not low enough for super-efficient in-ears, but it is close. It'll probably suffice for 95% of all in-ears around.

Using the STX II for gaming is a pleasant experience, although there are no big noticeable differences to the STX, which is good since it was one of the best sound cards around for gaming with headphones. The STX II now comes fully equipped to handle a 7.1 system, which I am sure is a welcome addition to both home-theater geeks and gamers alike. If you have a gaming den with 5.1 or 7.1, the STX II is a good collaborator.