I can't decide on the 16k, I keep switching between -3 and -9 (I can barely hear those frequencies and honestly don't care to). I definitely lose more sound dropping the 8k but I can listen for much longer without being fatigued. I wasn't trying to stir the pot, I was sharing what I found was necessary for me to be able enjoy them. The main thing I'm getting at is that sibilance isn't the end of the world after all. I've been doing a lot of A/B with my modded T50RP's and my HD580's without EQ and I still find the HE-400's brighter than both of them with my drastic EQ. I'll be honest, I definitely had thoughts of returning them initially. I have managed to stay away from EQ up until this point, so I was scared of it (haha).
Needless to say, I am absolutely digging these cans. I'm very impressed with them; they sound very unique compared to my other headphones and it's a very enjoyable change.