For informing any future suggestions: Why did you choose to sell your HE-400s?

just needed the cash :/

TBH, I don't think you're going to get much better than the HE-400s for solid bass & sub-bass around $200, unless somebody else I'm unaware of is making inexpensive magnetic planars in the same price range. Even the best engineered dynamic driver headphones (i.e. every Sennheiser model) just can't compete below 100Hz. The one thing the Hifimans won't give you is a wide sound-stage, but I'm sure you already know that, having owned a pair. You might look on the Head-Fi classifieds for a well-kept used pair.

I took a look at the 598s along with the ad900x and they both seem really bright. Do you know of a pair of cans with more bass but with the same quality as the two?

I suggest the Beyerdynamic DT880 Pro 250 Ohm semi-open headphones. On Amazon, you can buy the Beyer DT880 Pro for ~$230 new currently. These headphones are designed for tracking, and mixing; the frequency response is flat, with a crisp, fantastic bass response. The soundstage is excellent.

I currently use the Beyer DT880 Pro 250 Ohm w/ a Schiit Audio Modi 2 DAC, and Magni 2 Amp as a stack. I have no complaints about the sound quality of these headphones what-so-ever.

Nothing can beat beyer in comfort, but i feel like the bass is just not as punchy as id like in those

DT770 has loads of bass (closed though). DT990 comes pretty close in amount of bass, is fully open and fits your budget.

I hear that the 990 is a very V-shaped haedphone. Do you think the 880 would perform better for my needs?

K7XX's, there's new batch on massdrop atm.
Can't get better soundstage on that budget.

Well they aren't exactly bassy but they pack more punch than Q701/K702/K701

I will vouch for k7xx any day

best value in headphones

I have ATH-m50X's and like them quite a bit. I've seen them go for as low as $100. I actually kinda got mine for less than that. I got them bundled with an audio recorder, and I sold the recorder and ended up with the headphones for about $50, which is a steal. If you are patient and can wait 1-2 months for a deal, I'd suggest going to slickdeals.net signing up and then putting a deal alert in for some headphones that you are interested in, then it will email you when something pops up.

Ive had these. They are OK.

Ive heard that these are super bright and are for more female vocal genres. How do they do with deeper genres?

"bright" might be the wrong word to describe them, i would say they are clinically neutral.
I haven't had a chance to try the k7xx's but i own k702's myself and with bit of an EQ the lack of bass doesn't bother me,
If you have a chance to go and try any of the top end akg's you'll get the idea how k7xx's will sound like.

i bought the dt990 pro, they're really comfortable initially and long-term, though you might run into issues with the earpads getting in contact with your ears if they're really big

they also sound really interesting, both the treble and bass speak for these headphones (which is fine if you like it) and playing from a source like the schiit magni 2 they're both adjustable

http://www.head-fi.org/t/526839/dt880-vs-dt990-comparison-review
this is a "decent" comparison between the dt880 and the dt990 (edition 2005 and pro dont make a difference in sound), but the guy is overexaggerating on the treble on the dt990. if you have a chance to try them, you will either hate them or love them

I also have the 250ohm dt880s. Great headphones.

How hard are these to drive?

Not hard at all, they do like little amping and Magni2 should be more than enough.

they are less bright than he-400

they are sonically pretty similar to the he-400, actually, but a little less "sizzly"

My only problem with the 7xx is that I have to wait almost a whole month for them to arrive. In that case, I might as well get the Sony MDR MA900