Well it depends on how loud you want the kemper to be...
If you turn the master-volume knob the dB goes towards 0. You also have to check which volumes are linked to the master volume. If you want to control both volumes (main and monitor) with the master volume you might want to set them both to the same value.
I think my Main Out is set to -20 dB or something like that. I just leave it there, so the FOH always gets the same signal-strength. The Master-Volume is only linked to the Monitor out to control my monitor-cab on stage.
Does that help you?
You can return to the factory default settings by using the "intialise global settings" function in the system menu.
My output settings are around these numbers I think 0db is flat out and I don't think you want it to be that buddy as most FOH engineers moan that the signal is to hot 
To compliment the above posts, you can disregard the relationship between the used PUs and the output level. This is a matter that mainly involves the input section.
if you aim at different PUs to affect the output level, work on the input settings and/or on the rig level
HTH
I'm not near my Kemper right now, But those settings seem close to what I use
Thanks for the replies guys.
The point being no one has said what is the definitive setting, what is factory default setting?
Geezer
The "default" would be 0 dB. Leaving the outputs at 0 dB means the Kemper will put out a maximum of +22 dBu for XLR outputs and +16 dBu for 1/4" jack. If what you're plugging into can handle these levels, just leave the Kemper at 0 dB. But...unless you're plugging into a line level interface, you'll usually have to attenuate the outputs (e.g. when going XLR into a mixer). How much you need to attenuate depends on where you're going 
I had the same question and couldn't get a unique answer of this great Forum.
So I went with -15 dB for the Main Output (for the FoH) which enables to give a bit more Level (when needed) and on the other Hand delivers enough headroom for nearly all of the (professional and shared) profiles.
Despite of this, it still takes pretty much time to tweak the volumes (solo rhythm Change a.s.o.) of the used rigs in a Performance for live-use.
Thanks for the replies guys.
The point being no one has said what is the definitive setting, what is factory default setting?
Geezer
If you had tried the init global function you would see that the default setting is -12dB.
I did a Factory Reinitialize, and my main and monitor output volumes say -20.2 db.
I did a Factory Reinitialize, and my main and monitor output volumes say -20.2 db.
Not sure what "Factory Reinitialize" you tried but when you use the init globals function on page one of the system menu you will get the standard output settings which are -12 dB in the current version of the operating system.
I think I see the issue. The output vols are linked and was showing where the vol was set for the last Profile I was checking out. All good now.
no matter if volumes are linked-the state of the output volumes is never stored with a rig since all output settings are global. Only the rig volume gets stored along with the rig.
Maybe you touched the master volume knob when you clicked on the output menu button-that would explain it.
