I have owned M50 but I sold them quite quickly due to lack of bass for my taste but yea I'm a basshead. The bass is in IMO only relatively lightly boosted to the point it will never overpower the rest at all and it's recommended so often here for it's versatility, works "good" for most genres, not bad and not superb in any just decent/good for all genres. I was personally dissappointed with soundstage though, the XB500 has better soundstage of those two since it's not fully closed due to having some bassvents at back of the cups and this makes the XB500 sound a bit "airier" in comparision.
As for EQu... I'll let the following video speak for itself, the author is also among the most helpful people I've seen and he gladly tries to add features that his customers are requesting for and he's very kind, it's some of the best $3 you could ever spend owning an iPod Touch. Yes it's more than capable of doing what I was talking about:
Here's also my recommended EQ curve for XB500: