Something durable, with good bass and sub-bass, no harsh treble (I can hardly enjoy my **** 4in1 because of that) and
definitely something a bit different compared to my over-year HD650s in overall sound type. Detachable cable is a must as well (although in that price range I'm expecting that to be something common).
Thing is that I listen to all kinds of music, so can't specify just one type that I want to enjoy the most e.g. metal or pop. Want the headphones to be versatile
That's about it I think ...
P.S. Oh ... and one more really important thing. Because I'm using a desktop amp/dac combo, I'm not planing on spending more money into a DAP, so my new IEM pair should sound good enough with my mobile phone. Yeah, I know it will benefit from a separate DAP, but don't want that to be mandatory.