[klminch]

I've had my ATH A900xs for about 2 years now, but I've been wanting to get an open pair of headphones, but I don't know which to buy.  There are no stores around where I live so I could try some of these for myself, so I need some help on figuring out what I should get. 

As for what I'd use them for, I listen to a ton of music (basically everything except rap), play a lot of video games, and watch movies.  So basically, I'd use them for everything.  I really want a big sound stage and what I'm listening to to be really clear (like hearing different instruments in music, or footsteps in a video game).  I'm not a bass head so I'm not too concerned if it is a little lacking.
 
I was wondering if anyone had experience with any of the headphones I've listed above, or has other recommendations, that would be what i'm looking for.  Currently I'm leaning toward the akg q 701s, but am open to change my mind.  Also, as a side note, I do already have a mixamp pro with my current headsets, so I'm not concerned about the extra cost for an amp (unless it isn't powerful enough, let me know!).

 

[TiTaN]

From what I've read, the HE-400 should easily beat out the other two, but for $299 currently, twice the price the others have been sold for this month, they very well should.
 
In my recent (the last few months) experience, the Q701 with a good amp will beat the HD598 in pretty much every way, bass, accuracy, soundstage, etc.
 
I just returned my second attempt at the HD598's and was about to purchase the Q701 from a popular groupbuy site currently available for $149, if that tells you anything.

 

[PurpleAngel]

  I've had my ATH A900Xs for about 2 years now,
I do already have a mix-amp pro with my current headsets, so I'm not concerned about the extra cost for an amp (unless it isn't powerful enough, let me know!).

 
What sources do you currently plug the Astro Mix-amp into?
Is this audio setup for PCs or gaming consoles or other?

 

[klminch]

I typically just plug my current headphones into my laptop since they don't need an amp.  My mixamp is for my ps4 and my gaming headsets.  However the mixamp is compatible with my PC through USB.

 

[PurpleAngel]

  I typically just plug my current headphones into my laptop since they don't need an amp.  My mix-amp is for my PS4 and my gaming headsets.  However the mixamp is compatible with my PC through USB.

 
You might read up and ask questions on this site to see if the Astro Mix-amp is good enough for driving the Q701s
Might have to daisy chain a Schiit Magni headphone amplifier ($99) to the Mix-amp
http://www.head-fi.org/t/582276/q701-appreciation-thread
 
Might also consider getting some Hifiman HE Velour ear pads ($10+shipping) for the ATH-A900X headphones.
I really like my A900Xs, great for music, the Mix-amp might be the weak link in your music audio quality.
 
The mix-amp is a great match for use with gaming consoles, but you might look into a better DAC/Amp for use with the PC,
something to improve music audio quality, FiiO is coming out with their new E10K.