Have you seen the TV series LOST? Because I am now in it.
I have Kemper Main Outs using TS cables to my Interface. I have my Kemper main output volume level at -12db. If I raise it to max at 0.0db then my signal will clip inside my DAW... but then all I would have to do is lower the gain knobs on my interface to compensate to get the signal to fall back into the (-12db to -6db) recording range. Vice-versa on this if I lower main output level down to -66db (before infinity).
So what is the optimal main output db to go into DAW to get optimal tone, or is the optimal tone there no matter the signal strength?
It's just a matter of analog gain staging. Avoiding unnecessary gain/attenuation. It's not a good idea to attenuate the Kemper's output...just to bring it back up by adding gain on the next stage (interface).
If possible, leave the Kemper output at 0 dB (no attenuation) and don't add gain (noise) at the interface.