I am totaly new with Artis and got my piano today

When i finished unpacked I plugged in headphones and everything sound perfect. Then I want to test it with my mixer. I used audio out L/R in the back of the Artis and connected the piano to the mixer with new and high quality balanced cables. It was no sound!!!

I have tried different things:

- Used another cable
- Used another input on mixer
- Tested the mix input with another device
- System reset
- OS upgrade to latest version
- Checked volume sliders

Any idea what I do wrong?