Update: Got the Stax 4.5V adapter off Audiocubes along with a step-down transformer, and found that this also goes a very long way in eliminating the treble roll-off. The treble is still slightly recessed, but only slightly. I no longer feel like there's anything missing.
I think two things overall contributed to the treble roll-off:
1) Poor interconnects squelch micro-detail, and since the treble is fairly recessed at high frequencies, it gets squelched as well. Improving interconnects really improves the treble.
2) Insufficient power through the amplifier will manifest itself in a rolled-off treble and a flatter, more 2-d presentation. When using the power supply, the sound opens up and becomes much more 3-dimensional, with good soundstaging and imaging, although still it can't get over the "head full of sound" effect that canalphones produce. I've noticed that, when battery powered, the sound didn't really "open up" until the volume was at the 2:00 position, at which point my ears started to protest. At 3:00 the sound was pretty 3-d and the treble wasn't bad, but I wasn't going to listen to them like this, unless I had quiet(er) recordings. This is definitely unfortunate, since when you go quieter, you start losing treble and soundstaging. However, with the adapter, the sound is pretty open all the way down - definitely an improvement, and I'm pretty sure this is how these were meant to sound in the first place.
So: after a few months of ownership, what do I think of these?
Well, for a start, the more I listen to them, the more I like them. They do have a very unique sound signature (I'm not nearly as much of a noob as I was when I first got them, and I've improved my source quite a bit besides, so I'm a bit more qualified to judge). As bangraman said, strong bass, fluid mids, and (slightly) recessed treble, combined with a typical electrostatic presentation, make for a very interesting and unique sound. With some things, it does wonders - electronica sounds simply superb, as long as it is well recorded. Shpongle is beautiful, with full, flowing basslines, liquid, transparent mids, and treble that is very sharp and detailed. Ditto for Future Sound of London - every beat sounds crystalline in it's perfection, and you're lost in an ambient, 3-dimensional sea of sound. Really, for a $239 product, this sounds awesome. It'll take many times this much cash in amps and headphones to beat this kind of sound. Not to make this sound like it's the end of the line as far as quality goes, but it's one hell of a bargain.
But, some things sound not so good. Dark Side of the Moon is beautiful in most respects, with Gilmour's guitar sending chills up my spine, but the cymbal impact is missing. The sound is there, and you get most of the cymbal body with fairly well rendered reverberations, but it's quiet, far too quiet. Almost feels like the drums/cymbals are 30 feet behind the stage, and get overwhelmed by the other instruments. A somewhat uneven presentation, with a mix of gorgeous bass/vocals/guitars, and then this problem - although it's not that major, especially with all the right hookups. Some overly sibilant recordings that otherwise sound pretty good - like Porcupine Tree's "Up The Downstair," actually become more listenable. Still, it's rare to have a recording where the only problem is overbearing sibilance, and usually it is symptomatic of shoddy production across the board, which this thing will mercilessly reveal. However, there's enough treble with the AC adapter to give classical recordings the extra sparkle that is missing in battery operation. It won't fully give the effect, but enough that you stop hearing any deficiency without focusing on it too hard.
What I love most about this thing is the way in which it handles micro-details. My source is pretty good now, same for the IC's, and they're fully burned in at this point, so I think I'm getting as much detail out of them as I'll get without investing in a really high-end player. They're supremely detailed, but unlike, say, the ER-4, they don't shove the details right in your face in what seems to me an overly artificial manner (my 590's do this also - shove details in your face that is, although they're not even close to the Stax in detail). When listening to extremely detailed music (like Shpongle), I feel almost as if I have the ability to mentally "zoom in" on one specific layer of sound or detail, and listen to it at the exclusion of other aspects of the music, or I can "zoom out," and choose to focus on the overall sound, letting the sonic minutae slip past without pulling away my attention. When listening to other equipment that's overly upfront with it's detail, I get fatigued pretty fast, and I feel overall musicality is sacrificed in favor of the most detailed, analytical sound possible.
In this respect, the Stax gives you the best of both worlds. Detail and musicality, depending on what you choose to focus on.
I'm guessing this is purely an electrostatic thing, and is true for really high-end dynamic setups as well (which I have yet to hear). Now that I've heard this type of sound, I don't think I'll enjoy music as much without it. My speaker setup is pretty good for mid-fi (hey, when you get a $2200 setup for $500 used, I'm not complaining), but it can't even touch the Stax, especially in this respect (but it beats my 590's, although not by much).
I'm not in quite as much of a rush to upgrade now. I'll still get the 3030, but this thing I can live with, both at home and on the road.
Well, that's about all for now. This is a flawed product, but it can sound truly awesome with a bit of tweaking and attention. And, for what you get, you really can't beat the price.
