Very easy.
Your real input level depends on the Clean Sens parameter, and as Till says, you should set it up according to your pickups. The led above input will show when it's set up right - what you're aiming for basically is the led to be green all the time and maybe go a little amber/reddish when you hit your strings really hard. Everything is fine until you experience input clipping.
Distorted Sens is something that is adjusted to taste by yourself. If you feel like that your KPA rigs have overall less gain than you'd like, you raise it, if you feel the other way around, then you lower it. This simple.
Volume balancing should be easily achieved by the Cab/Amp volume controls, there's no need to touch the Sense values for this.