Thank you for your answer, you are right, if a virtual equalizer in the PC would be much more simple !
But the equalization is not the same in the headphones and in the amplified system.
In the headphones the sound is good, not in the speakers, and I don't want to change the sound of the headphones that I use most of the time.
On a complete mixer, ouput/Input for Aux often use cinch connections.
For the PC, I could too install a sound card more complete about in and outputs.
But anyway, the connection is a problem especially cause of the cinch input of my 3.1 system.
If I use the equalizer Jack ouputs, I know that Jack/cinch converters cables exist.
A TRS cable is a stereo Jack cable isn't it ?
I must think about all of that again...