Question about the speaker emulation

Welcome and yes the KPA sounds best without the speaker sim when using a real cabinet.

You find a lot of basic help here too:
http://www.wikpa.org/Main_Page

Hello FS,

actually you don't have to. I'd try and check what sounds best to my ears.
I've not used you cab, but I've had some good surprises by keeping cabs on with a guitar cab.
It won't hurt anyway

You will most probably get very clear responses from your rig

How better? With cab off I assume...