I'm currently looking for a good place to put around $250 between a couple of potential headphones or an amp.
 
At the moment I am using a pair of AKG K701s, and a pair of Beyer DT770 Pro 80s depending on what I'm doing/listening to.
Have an Essence STX with the headphone amp going through to the Beyers and the line-out going through a Firestone Cute Beyond for the AKG.
 
The AKGs are rather old (mid 2007) and though there don't seem to be any issues with the drivers, it's been showing it's age physically.
The Beyers are newer, however have a bit of subtle buzzing on the low end occasionally after I was forced to remove a stray hair from the driver membrane for about the third time and a small hole developed. (Seemed unavoidable, unfortunately.)
 
So considering these two things, I am looking at three options:
1) Replace the aging K701s with a new pair of Q701s. I have heard reports of the Q701s having a better low end with a little less fatigue, and even newer K701s having better low end response considering the serial on mine is relatively low (154xx).
 
2) Replace the DT770s with a pair of DT990 Pro 250 or 600. I definitely enjoyed the DT770s as a more 'fun' option, however they lacked some of the clarity and mid response I enjoyed in my open sets.
 
3) Stick with the K701s, fix them up a bit, and grab a Matrix M-Stage amp to replace the Firestone Cute Beyond. I've heard these work very nicely with AKG.
 
Your thoughts?

Heya,
 
1) The Q701 is only slightly warmer, very subtle, if at all. If you truly love the K701 sound but want maybe a tiny smidge of more warmth, the Q701 would be a potential buy.
2) Maybe consider the Ultrasone HFI 2400 as well as the DT990 PRO.
3) Adding the Mstage, which costs as much as a new headphone, adds a touch of warmth, but the degree of which is not enough for me to suggest spending this kind of money for what an equalizer does for free, since you already have an amp.
 
It sounds like you're wanting to keep a big sound stage, while adding some warmth. I would say the next headphone for you, with no gear swap, is the Sony MA900.
 
Very best,