K550's soundstage trumps the other two by a good margin. It's the least fatiguing of the three to listen to. It has the best overall balance. Only gripe I have is the fit. I wish it clamped a little harder so I can get better isolation and better bass presence. So far I like it better than the other two. It really does have the soundstage of an open can. Technically not as crystal clear as the T70 and doesn't have that kick in the bass of the 900's but it possess an even balance which I appreciate. Very comfy also. The isolation is on par with the other two and possibly better if you can achieve the right fit. I listen to just about every kind of music and my collection is on shuffle all the time, so I've heard everything on them so far and find that it works with most genres better than the other two also. I would recommend the K550 over the other two from aesthetics, comfort and sound all together. Another thing to note is that the K550 is not as exciting as the other two. Now, I'm just making this confusing and though. Sorry.
Thank you for the informative reply.
Have you tried bending the head band to increase the clamping force and so the bass too?
Oh, and as I was reading your post I really got excited and I was all set to place an order....that's until I read your last sentence