Your mistake is to think that a maximized soundstage width is desirable, moreover one with an unnatural feature: extreme channel separation at low frequencies. When I'm talking of «preserved» of «improved» soundstage I'm addressing lifelikeness, credibility and threedimensionality. A hard-panned recording doesn't provide this, despite the wide soundstage. Note that it suffices to reduce channel separation at low frequencies, so you don't lose any essential spatial cues.
I don't understand your question concerning the «STX». An Asus soundcard? I can't speak for it. As to measuring sound quality: Without any extreme measuring data you can't predict the sonic characteristic or the sound quality of an electronics device. The only data I'd consider extreme with the HM-801 is the treble roll-off. Everything else is decent and below the established hearing threshold. Sound quality can effectively only be judged by ear.