Thanks for your answer Doc, I did what you said (turned the pre amp signal up and the mixer signal down) and it gave a great result when listening to it from the mixer monitor.
The problem still left is the signal that is transfered to the computer!!

Output from the computer to the mixer works perfect and gives a 100% clean sound, but when recording I get a strange almost mechanical twist of the sound plus there is a low frequenze constant buzz which is not there when just playing the guitar using monitor sound!!

I tryed using Cubase SX but it wanted to update its setting due to the new audio path I created. The update failed since a hell lot of 'Sync' were lost, I have absoluttely no idea what that means but maybe you can make something out of it?

Thanks once again for reading