Long time lurker looking for a set of good over ear headphones...

Preferred genres? SQ preferences? Portable? Home? Is comfort important? Is isolation important? 

HD558/598s are fantastic all-rounders. Better than the HD555s I had for a while. The bass doesn't extend that low for dubstep, though. My HD580s are good all-rounders as well, but again, they might not do so well for dubstep. People cite them as some of the best gaming headphones you can get. If you can stretch your budget, the D2000s have fantastic bass extension, not too colored so that they wouldn't do well as an all-rounder. The soundstage is pretty large for a closed can, and they reportedly are good gaming cans. This thread has some really nice review/comparisons on gaming cans: http://www.head-fi.org/t/534479/mad-lust-envys-headphone-gaming-guide-updated-9-29-2012-he-400-edited

I strongly suggest the Ultrasone Pro550. They will suit your needs of gaming/bass perfectly. 

The 558s are pretty similar to 598s in sound, some argue with mods, they can be nearly identical. I wouldn't know by experience, so don't take my word for it. I happen to really dig the HD598's looks, but I wouldn't want it to be my only pair. The 770PROs have immensely satisfying bass, quality is phenomenal. But not that great of an all-rounder. They also isolate and are really comfortable, perfect for portable use, albeit a bit large (I know you said you would use them for home, but versatility is always nice). Haven't heard the M50s or K271s, sorry.

One other thing would be to get a used HD580 on ebay. They go for ~$100 US nowadays, so you can fit some sort of amp/dac combo into your budget. They are an older version of the HD600s, and with grills replaced and new pads, should sound identical to a HD600 with non-revised drivers (heard a newer HD600 pair, they had slightly more treble, otherwise the same). For more info, just go look for reviews of the HD600s - there's more than plenty. I can say that they are solid gaming phones, fantastic all-rounders, and comfort/non-fatigue levels are off the charts good.

If you want them to be portable, then you can count out the 558's for sure. That said, they are a very good 'phone for home use and work reasonably well for gaming. With the tape mod (easy to do: http://www.youtube.com/watch?v=PvQ8PzBrHXE) they gain a little bass impact which would be good for your dub step. DT770 or the DT990 are both great gaming cans, with sizeable bass impact and detail. The M50's are great portable cans and are more comparable to the DTXX0's than the 558's. Cant comment on the Akg's as i havent heard them, so i'll leave them for others. For gaming, the beyers probably edge out the 558's at that price level. The akg's and m50's are at a cheaper price level, and i cant really pass judgement on which is better as i've only heard the m50's, which i must say i liked for the price. (Usually around $150 although they can be found cheaper)

I wouldnt use the M50 for gaming though, their soundstage is terrible. 

They should be fine with the soundcard. Won't lack in power. It'd be nice if you got something cheap, like the FiiO E17s, but not at all necessary.

I just bought myself a pair of DT770 pro 250 ohms, I think they're wonderful. 

They're pretty versatile all around, I use them for gaming, music, and movies. I'm also an avid listener of dubstep and I have to say the 770s do a really nice job, they're not really heavy on the bass, but they're just on the point that they give a nice bang, but you can still hear the mids and the highs. 

I have to say I'm not very much knowledgeable on the technological terms of music, so I won't be able to give you any advice in that respect, but these were the first higher price grade cans I purchased (a week ago) and they've blown me away. I've chosen for the 250 ohm version, because they sound really good without an amp (imo) and they'll sound even better with an amp, when I finally get my money together for one, so the best of both worlds.

I don't know if Malveaux is going to post in this thread, but I've PMed him about my choice of cans, and he's the one that made me buy the DT770s and I must say I'm not regretting it.

They're within your price range, I think, I bought em off of Amazon for £126, but I see they're now £115 :(. 

Some other headphones I've considered were the DT990s, but they're open cans, so they'll leak sound like crazy, unlike the 770s, who are closed.

And the Brainwavz HM5 (from Amazon) (or from mp4nation, they come with a stand, and you have the option to select an amp). I haven't heard these myself, but I heard they're a real bang for your buck, thought a bit less bassy than the DT770s, more neutral, but then again, don't take my word for it, I haven't listened to them myself, this is just based on what I read.

Also, since you mentioned gaming, the mic I'll be getting to use with my DT770s is the Modmic, it's currently without a mute function, but they said that by the end of October they should be ready to start distributing the modmic with a mute function. I don't have it yet, but I'll be getting it for sure when the muteable version gets released.

Well.. That's my knowledge so far.

Good luck!

EDIT: Forgot about comfort, I'm using the stock earpads, that came with my pair, and they are pretty comfy, I get times that I just want to take them off for a few mins, but that's no biggy, I mean I can use that to go to the toilet or something, rest my eyes a few seconds. I haven't tried any other pads, but I know they're out there. So in short, they're really comfy, but I have had a few times that I wanted to take em off for a few mins and do something else because they were getting a bit annoying, this was after  a good number of hours though, mind you.