Torn between what to buy

Denon C710, C751 or Panasonic HJE900

I think you ought to consider the Fischer Eterna's, which are some of the funnest IEM'S I've ever used. It seems they adapt to almost anything you throw at them and with your taste in music I imagine the emotion and fun factor supersedes the need for transparency and upper range detail. 

Also, see if you can snag a refurbished Monster Copper from MobilePC, which recently had them at around $99 with free shipping. I have received an open box TF10's and the original Turbines from them, both heavily discounted and both, after meticulous study, contained every retail accessory and passed possible counterfeit analysis, 

Personally, I only own the S4s off your list.  I'm looking to upgrade from them now, but I have to admit that I'm very impressed with their performance.

I use them when walking to work and while at work to drown out some of the surrounding office noise.  They have an excellent range and sound great.  For the money ($80 or so at my last check without the mic/iPod controls, $100 with), I don't think you can go wrong!

I should also mention that I, too, listen to Dubstep, House and other electronica.  These 'phones handle all of them fairly well (especially considering the price).  If you're in the US, you can pick them up at Best Buy at fairly competitive prices and give them a try.  I suggest living with any headphones you choose for 1 to 2 weeks (unless they're completely uncomfortable) to get used to them before making a final decision.  

You can also find Triple Fi 10's on the FS forum for near $100, usually hovering around $120-130, but well worth the price. They remain the funnest IEM'S I've ever heard and particularly excel at musically fast genres.