got my pair about 2 weeks ago. Gave them a small overhaul (cleaned them), and been listening to these since. They are VERY precise, which might not be everyones taste. This might also be their only flaw, because not many people will like them for that. Build quality is very nice, standard for top of the range AKGs. They had maintenance in mind when designing and building them.
Havent had a chance to compare them directly to K70x, but from what most people say - K500 should be more enjoyable to listen, more relaxed.
While I had my pair, I mostly listened to instrumental and prog rock, classical also. I found them more than good enoug for my taste. And extremely comfortable. Even so much that I would forget I had full size headphones on my head and almost doze of on the the side of my pillow...