I have A/B numerous times between K550 and Q701 using E17. It seemed that the bass boosted on K550 is of lower frequency giving more impact while Q701 are of slightly higher frequency where it is louder but less impactful.
If you perform some critical listening, you may notice Q701 has higher resolution and detail in the treble range. While K550 comparatively is a little less resolving, ie sounds doesn't sounds as true. But you have to be really picky and focus to pick out the difference. (cymbal, hit hat...)
The above observation is subject to change as it is based on a pretty well seasoned K550 and a fairly new Q701.
Also, K550 is less picky in listening environment. I can completely immersed and enjoy the smooth and clear sound anywhere. While for the Q701, because of the open nature, the sound signature changes drastically depends on background noise, type of room, size of room .....
Both HP are wonderful!
There sound changes depending on room size and type? Aren't you exaggerating?