I know that these two headphones are quite a different design and the AD700s are open back and the K550s fully closed.
I think one of the main reasons that I would like the K550s sometime is because I think their isolation should be a lot better than my others. I don't mind so much hearing sounds from around me but I find it hard listening to music on my AD700s without people around me hearing what I am listening to. I can't complain about that though because they are open back and that is what makes them sound so detailed. The other improvement about the K550s is that there should be a big increase in the amount of bass in comparison with the AD700s. At the moment, because the bass is quite lacking, I am using a Fiio D03K and also, the Fiio E11 which I boost the bass on. Even now though, they still don't sound very powerful. I have been very impressed with the detail from my AD700s and I really like the bright sounding treble. From what I have read, the K550s have an incredible amount of detail and an open and airy soundstage considering they are a closed-back design.
I live in the UK and one of my local stores have them at £129 and they also say that they should be able to beat other online places that sell them.
I should be able to go and hear what these headphones sound like at this store.
If anybody has both of these headphones or even one or the other, could you give me a bit more information about the K550 or comparing them both.