I have the ES5's. Jude has both the ES5's and the custom variation of these as well, which should be similar. I'm not really comfortable giving detailed comparisons yet as I've only listened to the 334's for maybe two hours in total. I'm pretty sure the 334's image better, though -- it's definitely a larger image, at least. I don't mean to parrot MuppetFace, but, having heard a pair now, I'd have to agree that the 334's feel like little SR009's. The ES5's are more like LCD-2 r.2's. So, they're both smooth, but the 334's achieve such smoothness with less coloration, I guess.
They're also both notable for their midrange performance, but the 334's are more, how would I put this... liquid?