[Kilment]

I have used the DT880's (250 OHM) for quite a while. I love how comfortable they are, but looking to see if I can find a better pair of headphones for under $400.  Will be pairing with a schiit modi 2 + magni 2 stack. I primarily listen to pop, EDM, rap, and classical music. Thanks for any suggestions.

 

[KG Jag]

The one you have is too close to the 600 Ohm version to justify anywhere near $400.  You're much better off using it for a complimentary can or just keeping it in your pocket.

 

[Youth]

Not sure if T90 is considered an upgrade from DT880 but check them out.

 

[Kilment]

They seem to be out of my price range. Anyone know anything about the HD 600's?

 

[KG Jag]

  They seem to be out of my price range. Anyone know anything about the HD 600's?

 
Excellent cans and a good complement to what you have.  See:
 
http://www.head-fi.org/t/634201/battle-of-the-flagships-58-headphones-compared-update-audeze-lcd-2-revision-2-6-4-13#user_HD600