If you wouldn't mind....
I currently own the Koss Porta Pro, loving the sound quality and especially the bass impact for the most part, the only two caveats being that I wish the soundstage was wider/grander and also the fact that these phones are not comfy over ears.
That being said, ideally, the headphones I'm looking for are to be open backed and circumaural over ears.....with detail, clarity and bass impact....I also do not think that I am sensitive to treble.
Also I will be getting the Xonar Essence ST sound card to use as my source and although it has an amp on it I plan to buy a seperate dedicated headphone amp (tube or otherwise) a little later down the line.
So the three Beyerdynamic headphones on my list currently are the DT 770 Pro (250ohm), the DT 990 Pro (250ohm) or the DT 880 Premium.
Currently there is a price difference of £40 between the 3 headphones, the DT 990 being £40 dearer than the rest with the DT 880 being a refurbished model and maybe representing something of a bargain.
In any case the only thing putting me off the DT880 is the fact that I read there is a lack of bass impact but on the other hand I read they are super clear and detailed, basically I'm undecided between the DT880 Premium and the DT990 Pro.....really like the Koss Porta Pro sound that I currently own but I want comfy over ears again....music I listen to is mostly rock with some electronica thrown in....I'd also be watching movies and playing games through these headphones.
So not sure which one to punt for, I'm thinking the DT 880's because I could conceivably profit on them if I didn't like them, but I change my mind daily between the headphones. I'll either love or hate the DT 880's that's one thing I will say. Not that I'm a basshead in particular I love clarity and detail just as much if not more it's just I do notice when the bass impact is lacking.