I've only briefly heard the ATH ES55, the S500 is closer to the ATH phones which has more mid bass, but I feel the S500 sub-bass goes deeper. S500's Mids and Highs are a couple notches above the ATH.
The S400 are more balanced sounding to me and are outstanding because nothing is lacking just as nothing is overwhelming but when called upon, their sub-bass matches that of the S500.
So are you implying, although the es55 costs double the price, the s500 and s400 are the better hp's? I don't like thumpy bass, I'd rather want it to be deep and feeling it, rather than hearing it. I've owned the m50 and hated it, totally overrated. Fun, transparent and engaging are my keywords.