Mega bass is crap, complete, utter crap on modern CD players.
On my old Sony D-242, however, the mega bass performs quite nicely on the "Mid" setting for thin sounding recordings. I don't use it at all (I only use the line out, which is a real line out), but with cheap headphones it can actually help the sound, amazingly enough. On my HD600s, ampless out of the D-242, they go from sounding thin and grainy to sounding a bit wooly, and more thumpy, but not too excessively so. On the max setting they are getting boomy, but still less so then on the only mega bass setting on my cheap Panasonic player.
Why don't they make players like this anymore? The D-242 can almost drive my HD600s acceptably, with the mega bass on mid they sound more full then on my Airhead, but also a bit boomier, and the player itself can drive them to downright loud levels.