Wavedrum and AVID MBox - no sound

[manuvale]

Hi to all, I hope someone can help me with this issue. When I connect my Wavedrum to my Audio Interface (AVID MBox) I get no sound. I tried all connection modes. I can't figure out why it is not working. If I plug in my headphones to the WD there is sound, but there is no sound from my monitors connected to the AVID Mbox. Even if I connect the headphones to the phones output of the MBox I cannot hear anything. I read some topics about preamps so I tried to connect my WD first to a Dual Channel Pro from K6K Sound and the output of the preamp to my AI input. But this did not solve the problem.
Does anyone have a solution?