So, I´ve tried the Y cable I had around it solves the issue!
That said, when I have Cubase on, the signal is pretty high and I when I hit the drums hard, it clips. However, the volume is lower than the volume I get when connecting the headphones drectly to the drums. I´m using inputs 3 and 4 at -10 db, should I change it to +4db?
Also, looking closely at the stereo singal level in the stereo track, the L bar goes higher than the R bar; is this correct or L and R should have the same level?
Thanks a lot for finding the main issue!!