That is true. I also always believed the ST is very good, and on first hand, when compared briefly to my Musical Fidelity M1DAC, I thought it was as good, didn't really feel the M1 is worth 4 times as much. I usually use the M1 in my speaker setup, while the ST is only for my PC, which is the only place where I actually use headphones. However, every time I do a more deep and detailed comparison between the two, its clear why the M1 is more expensive. It simply sounds better. As time goes by, I like the ST less. Its good technically, its got the clarity and detail, but its just...wrong somehow. It doesn't make the music sound enjoyable, its too rough in the high end, soundstage is not all that big, bass is quite lacking and overall as you said the sound is somewhat congested. And thats not immediately noticeable. I used to compare DAC's by taking a 20 sec segment of music, such as a acoustic guitar, or some vocal, and then I'd loop it and compare on my amps with 2 inputs, and I'd always walk away feeling they sound identical. Well, thats because my methodology of testing was totally wrong. What I should have done is picked up the most busy, congested, messy track of some classical or metal, or rock music, something with a lot of things going on...THAT'S where the difference between a cheap and expensive DAC comes out. It's easy to reproduce a flat frequency response and be technically good, which will make the sound appear good, but there are things that are harder to measure, or not possible at all to measure, and aren't included on the list of features on the back of the box. It's not all about technical measurement either.
For example, ST's DAC measures better than M1DAC on all aspects, looking at the paper data, you'd think the ST is superior. Yet, listening to both, there's no doubt which one is better. Same with the headphone amp section. It totally outclasses most standalone amps in terms of measurements, yet, even a cheap Musical Fidelity V-CAN sounds worlds better, so much more spacious, smooth, effortless with more air in the sound, separating everything apart while making it sound more musical at the same time.
Oh, and just to add, my findings are with LM49860 or LM49820 in the buffer section, and 2x dual AD797BRZ or 2x LM49820 in the I/V.
Not saying ST / STX is bad, its still most probably the best DAC/amp combo you can get 200 dollars, especially considering its versatility in terms of various dolby features for movies and games that really make a huge difference, but it's wrong to say it's a giant killer or that it can compete with more expensive gear. I used to say it as well, but I eat my own words now.
I'll be checking eBay® for appropriate adapter PCB's to fully tune the same vendor's LME49990MA (which appears to be a direct descendant of the LM318AN high-performance op amp from the equivalent schematic) as a package with surface-mounted compensation filters for the line-level buffer - I have both a Hewlett-Packard® HP2009m display with internal speakers and a Pyle® PCA2 offboard 40Wx2 amplifier for bookshelf speakers that my STX can drive via the dual-RCA output jacks.
i might use it just for the day 
