[money4me247]

  Well guess I have to narrow it down to the dt770s or the dt990s. Are the 990s also in need of an amp to bring out their ''potential''?

if you are considering the open high impedance beyer dt-990, I would also look into other open high impedance options offered by sennheiser (such as the open hd598 at $180ish), akg (such as the open q701 at $190 or k702 at $220, or k612 pro at $169).
 
The AKG K550 is a closed non-portable pair of headphones that are sub-$200 that sound pretty amazing that has a low enough impedance to not require an amplifier.

 

[some1else]

Forgot to mention that $200 is the budget only for the headphones. I don't mind spending an extra $100-150 on an amp.