The FX500s have loads of bass presence, more of the sub bass than the midbass that's characteristic of the IE8s and DDMs. I suppose bass texture won't be that much of a concern listening to hiphop or electronica but as I listen to classical mostly through them when on the go, it has to be said: that's what I love the most about the FX500s. The texture contributes significantly to the great timbre that the FX500s are known for. They're quite sibilant though. I don't know how that'll affect your type of music, given that my music preferences exclude hiphop and electronica.
I got to audition the DDMs for about an hour today and I have to say, I wasn't all impressed by them. They had loads of bass, no doubt, but the DDMs just seemed so muddy and confused compared to the FX500s. I've read reviews extolling their bass texture but I just couldn't make that out earlier today. Maybe I'm just spoiled by the FX500s, or maybe the listening environment wasn't optimal, or maybe I couldn't mate them with my ears properly. If you like your bass though (and that's all you care about - authoritative high end, fit, isolation and microphonics aside), then the DDMs are an easy recommendation.
I can also vouch for the HJE900s being well-suited for more modern music genres. They hit hard enough when called for and they have an in-your-face type of presentation; gobs of midbass and a very fun sound signature. They also tend to be sibilant on some recordings, however, but not to the extent that the FX500s can be.
Btw, the person whose DDMs I auditioned earlier today also gave his impressions of the IE7s. They're more of a mid-centric deal, and have significantly less bass than the IE8s. He said they're better suited for classical music than more modern genres. I didn't get to listen to them though: he only brought the DDMs and SE530s with him. Re: the SE530s, well, that's a whole other story.
I hope this helps.
