Some news for those who could be interested.
I made some cross check with another stax earspeaker (SRM 600t) and found out that sound level was about the same.
Therefore i contacted stax in Japan to get some advise from them.
They have been perfect and took time to listen to me .
They found out that sound level out of my CD player was a bit to low (Rega Apollo 2V output signal) and recommended me to use a preamp
They recommended to me an Accuphase, which i finally bought.
I get now a perfect signal and sound level.
The quality is increadible !!
Thanks to all of you for your support