I’ve asked for that too without having a proper answer.
In my case, I first tried to export at -0,02dB but I noticed some clipping on bass files so I decided to try to export each track at -3dB (I put a dynamic plugin on master track on Cubase,).
But then I still didn’t get how to manage the mix, I’m on mac and uTool doesn’t work very well. I’m waiting for the new v2 that should solve problems.
Sorry for the delayed response I have overlooked your message somehow.
I made a test with full scale signal, I had no problem with this signal. I made a measurement on the outputs on the back panel.
This is true if you use full scale signal on each output that may overload the internal mixer.
You didn’t describe where do you experienced that clipping? If only in the headphones output you may need to reduce the levels in the mixer in uTool (let say -9dB on each track)