Just a quick followup on the difference is output from main to headphone outputs.
I hooked up the main L/R outputs to a stereo input (dual 1/4") into my Zed 10Fx.
Using the same headphones, the sound out of the headphone connection on the Kemper seems a little more "smooth" than the one on the ZED.... which seems a little crisper and perhaps a tiny bit more brittle.
I also noticed that once I evened out the volume into the headphones from the mixer so that it was about the same as the Kemper output, the difference was smaller .... but still there.
This could be just a difference in headphone drivers. It is pretty small.
Still have the bigger task of making my Kemper mix well with my band. That should be done by the middle of next week.