With the latest version of Dawn V2, I chose the Lower Gain setting (GMD = 2), which actually significantly reduces the hissing sound from very sensitive in-ear headphones.
As an indication, on the balanced output, with the Earsoncics Purple (very sensitive), I used to listen with a volume of 35 and now with a volume of 50.
With the Sony-IER M7, IEM requiring more power, I used to listen with the volume set to 56 and now to 70.
This comparison is necessarily very subjective and perfectible because once the parameter has been modified, you have to test using your memory only.
This new setting therefore seems very interesting to me for in-ear headphones because even if you have to push the volume higher, you still remain far from the maximum (and I have not yet checked the high gain).
I renew to you, Mr Walkman, my thanks for your very enthusiastic and ingenious work.