I buy headphones and all sorts of other items from Aliexpress all the time. They are as legit as they come. It is basically chinese ebay. Aliexpress' main company is Alibaba, which is huge.
Just keep in mind there are lots of knockoffs. The $30-40 IE80s for example. Not the real thing so don't expect it to be (and they say they aren't), but they actually do sound really good.
I started a chinese brand thread not too long ago on some of the other earphone/headphones available on it. Lots of good discoveries to be made that are practically unknown.