I can say it is just on the Fostex Hp A3 who use a Burr brown with an Akm chip,but on him for the first i find him good.
But with Time i found the the sound was two colered it.And find this not really good.
On the Fostex Hp A 4 Bl it was too and find some things not so good who the Fostex Hp A3 can do it better.
I am sure the problem is on the Ampification from this.
The Questyle Cma 400i looks better but never heard it.
Topping dx3 pro is sure good too.