[xTIRO]

I'm a novice audiophile and know a bit about headphones but not much. I currently own a pair of Audio Technica ATH-M50s but I'm looking to upgrade to another pair of around ear headphones that sound better. I was thinking about the Sennheiser HD 558s but I don't really know what else is out there. 
 
and I'm looking for a price range around $100-$300

 

[Trunks159]

Must it be open? What sound signature? Source?

Id recommend 2 headphones:
ATH WS99-has better and more forward mids than the m50, and much tighter bass, larger and deeper sound stage. Amp them and thell be even better.

Sony mdr ma900- It's open, unlike the ws99, and is a fanatic open can. The bass is very present for am open can, and the mids are just crystal clear. Largest sound stage I've ever heard. Also the most comfortable cans ever!