Help with an audio setup

Hello,
I am in need of some audio advice. I am looking to spend about $250 on an audio setup. I want to get a good pair of open-back headphones, and some kind of amp and dac combo unit to use instead of on-board stuff. I am looking at the dt990pro 250ohm, the HD 598 SE, and the ATH-AD900X headphones. Not sure if there are any other good options available. For a amp dac device I was looking at the fiio e10k or the creative sound blaster ZX. If anyone knows of anything better or a combination of headphones and amp/dac that works well together I would appreciate advice.

Thanks

O2 is $119, lots of people seem to like it, there's a portable version for a bit less

otherwise headphones aren't my thing I'm happy with my Superlux 668Bs which are like 40 bucks

here's the DAC AMP combo unit I guess, little over 200
https://www.mayflowerelectronics.com/shop/digital-to-analog-converters/objective2-with-odac/

Probably going to want to get your DAC/AMP before your high end headphones, so you start from the bottom up.

I have the hd 598 SE headphones and they're pretty awesome. super comfy, the sound is good for games/metal, and they feel premium. The sound stage is pretty open, though less open than something like the ATH 900x ones.

I have both the e10 (first version) and the e10k. They are absolutely incredible for the money.
They will definitely pull their weight with headphones up into the $500 range.

However, the "suitable impedance" listed in the spec says 16Ω~150Ω. You may want to look for a real powered headphone amp for something in that impedance range.

I have heard good things about the http://schiit.com/ combo.
Modi 2 (dac) + Magni 2 (amp)

BTW, this should be your primary source of audiophile reviews. http://www.head-fi.org/products/