blue2you:

I'm using the XLR male output (1) with a XLR female balanced than unbalanced cable (Vovox) that go to return of my amp.

Assuming that you mean "balanced then unbalanced", how are you connecting them so as to unbalance the balanced cable ? My guess is that you are just plugging one into the other, without any arrangement to unbalance the balanced line. In this case, one of the H8000 outputs will probably be blowing in the wind, which would cause your problem.

In your later post, you suggest following the instructions in the User Manual – I would encourage this.