Let me add something.
The enjoyment of listening to recordings with headphones (and speakers to a lesser extent) is based on an illusion. Sometimes, slight differences in the overall sound quality can help you to strenghten the illusion and make it more believable. Then you can say DT880 into E10 sounded good but just that, but DT880 into Yggy/Rag sounded like the real thing, and that's fine from an audiophile's perspective.
When it comes to describe sound in an relatively objective manner, I prefer to put things in context. A hall full of musicians is the real thing, a recording is not the real thing, although a good one can be close. Then most of the times (99% of the times) the recording was ment to be played on speakers where you have natural crossfeed. Then a good recording played trough quality speakers placed on a treated room will offer a soundstage that's relatively big and easy to believe. Then we go down into the headphone world where there's no natural crossfeed to speak of. Important part of the soundstage clues are lost in this case (headphones) and thus headphones are not close to speakers placed in the right place.
In that context, we are comparing the AKG Q701 which is one of the headphones with bigger soundstage, with Sennheiser HD800, probably the headphone with bigger soundstage. So, when you put things in perspective, these two are really close indeed. You can change the amplifier or DAC to tweak the sound a bit towards your preferences, improve/refine it a bit here and there, and make the illusion more realistic for you, but in the big scheme of things differences are still subtle.