I just thought i post this as I just answered someone's question regarding the Q701 versus the K550. I just thought I share my response here for future reference.
I did make a youtube video on this, please take a look:
However for more in-depth answer to the versus question, here was my answer:
For what sounds better?
I think it really depends on what you consider "better" on sound quality because they are very different headphones.
If you like your sound quality to be more relaxing, laid back, while providing a excellent presentation of depth and sub-bass, the K550 will fit your bill.
However, if you like your sound quality to be more analytical and detailed with a wider soundstage, the Q701 will be the one I go for.
If you like a combination of those two, i suggest looking at the HD800.
Which would I personally choose?
Personally, on one day I would prefer the K550 and on another I prefer the Q701. It really depends on my mood lol.
So it depends on my mood which headphone I will choose to listen to. That's why I have both!
Do take note though the K550 have fitting issues with some people's heads, while the Q701's fit is universal.
Please do take a look at the video for a more in-depth comparison. But feel free to drop me more questions.