@ecximer
Why do you need the gamma spinner?
The gamma should be set at 2.2 for work, and if you render in full float you will get an untoned exr image, after that apply your gamma in comp, since you have a full float image you can do whatever you want.
You should not be playing with gamma for correcting the render IMHO, you should get a linear full float image to work in comp.
Master Zap did a great post about this some years ago.
Cheers!