Pros: Beautiful material and construction. Excellent comfort. Warm, full-bodied mid-range great for vocal pieces.
Cons: Lower-treble issue. Tonality isn't as balanced or smooth as its cheaper cousin, the EM9d.
I purchased these for my wife two years ago. She's always liked the warm sound of my ATH-A9X, so for portable use I got her the ATH-EW9, which reportedly has a very sweet, warm mid-range.
Materials & Craftsmanship
The packaging is the same as other high-end Audio Technica clip-ons, which is to say I find them elegant and classy.
The headphones themselves are simply gorgeous. The Hokkaido cherry wood housing are perfectly finished and the 35mm stereo plug is elegantly shaped and endowed with the letter "ATH-EW9 JAPAN" printed in gold.
The included accessories aren't as luxurious as the headphones themselves, which was a little bit of a let-down. The carrying pouch is the same one that used by the lower-end models (EM7, EM9d, EM700, etc.), and the netting used on the inside is a bit on the rough side - I worry about it scratching the delicate wood housing (though so far it seems to have been fine).
The included extension cable is also the same one used by lower-end models - I wouldn't complain about it if the EW9 used the same kind of 35mm plug as on the other units, but they don't. As the result, the contrast in aesthetics is rather stark when the EW9 is plugged into the extension cable.
All Audio-Technica clip-on headphones are extremely comfortable in my opinion. They use a very unique type of earclip that's self-adjusting and doesn't put pressure on the ears, and the earpads are very thick and plush. I often forget that I am wearing them.
I actually have several gripes about the way the EW9 sounds, especially considering its price (about $200 retail, I think) as AT's flagship clip-on. It has a very thick and sweet mid-range, which is fine for those who likes this type of signature. However, I find the overall tonality to be peaky and problematic, particularly in the lower-treble region (seems to have a peak somewhere in the 4-8KHz region). There may possibly be some ringing issue, since the EW9 uses a closed-back design. In comparison, its cheaper cousin the EM9d (which I own, and much prefer) uses aluminum housing that's fully open-backed, and does not exhibit this symptom (the drivers on the two units are the same).
Treble: The treble extension should technically be the same as the EM9d, but subjectively it doesn't feel as good due to the mid-range being so dominant. The aforementioned lower-treble issue sometimes exhibits itself as sibilance, and other times as overly energetic "screechyness" (in string instruments for example). For vocals, this headphone is great - but instrument timbre simply isn't as natural as the EM9d.
Mid-Range: The mid-range is thick, warm, and very forward. Old-school AT fans may like this quality.
Bass: The bass has decent tightness and extension, though like the EM9d it is on the light side quantitatively.
Sound Stage: The sound stage on the EW9 sounds less open and more congested relative to the EM9d, both due to the treble issue and the closed-back design.
The ATH-EW9 is a very beautiful clip-on that's well-suited for certain types of music. But its high price and the uneven tonality limits its versatility - if you can find its cheaper cousin, the EM9d, I personally recommend going for that instead.