A's are really nice cymbals but I find they lack character a little. K's are definitely more complex, I guess it's something to do with the balance of the
Attack, wash, decay and the tones involved. It's hard to describe but K's have that beautiful wash that seems to linger and stamp their mark over what you play - at loud volumes they can swell like a tidal-wave and back off, at lower volumes the wash still hangs around and the
attack has a little bit of "push" so you feel like you're awakening something. Oh, and I would certainly use K's in any musical setting, death metal included - there are some heavy K's out there, I crash the living hell out of my K ride and it sounds great. More dynamics in metal!
I must say though, I'm finding that my K ride isn't ageing all that well. It seems to be choking up a bit whereas similar sounding Istanbul or Bosphorus cymbals sink gently into old age and really open up. I think it's Istanbul all the way for me from now on, you just can't go wrong.