I have to say that the sound with original opamps is the same than with my Topping E30 pro II, really good but same mood, à lot of clinical trebbles.
With the other opamp provided by Fosi as a gift, this is another color : the trebble is softer, the médium is forward with a magic warm, the bass is in perfect place.
This is less tiring for long hours of listening.
The change is a real thing, not a psychoacustic perception.