Pros: Beautiful material and construction. Excellent comfort. Warm, full-bodied mid-range great for vocal pieces.
Cons: Sibilant due to lower-treble issue. Treble extension isn't very good compared to its cheaper cousin, 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 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, it is extremely sibilant (seems to have a peak somewhere in the 4-8KHz region), the the mid-range/lower-treble has the tendency to dominate everything else. I actually much prefer the cheaper EM9d for its far more balanced tonality.
Treble: Treble extension doesn't seem as good as the EM9d, but since both headphones use the same drivers, I attribute the issue to the pronounced lower-treble peak (could be ringing caused by the housing material, too. I think aluminium may actually be more suitable for the housing of this particular driver).
Mid-Range: The mid-range is thick, full-bodied, and warm. Some old-school AT fans really like this signature, and I will say it delivers vocals very well.
Bass: The bass has decent tightness and extension, and complements the mid-range pretty well.
Sound Stage: The sound stage on the EW9 sounds less open and more congested relative to the EM9d, IMO due to the thick mid-range and the issues in the treble that I noted.
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.