@Ale,
Further to my previous post, I just wanted to add the following clarification...
When connecting your KPA to a traditional guitar cabinet, it is a general rule that you should turn off the Cab Module (cabinet simulation). However, every once in awhile you may find that you will prefer to have a particular Cabinet profile/sim enabled, when playing through a particular guitar cabinet.
When I first purchased my KPA PowerRack, I hadn't yet received my XiTone passive 1x12 FRFR monitor. So, I initially connected it and tested it with the following cabinets I own:
A) Marshall Vintage Modern 4x12 cabinet
B) Vox 2x12 cabinet
C) Tech 21 PE-60 Power Engine
Now, in the case "A" and "B", I definitely had the KPA's Cab Off. However, with "C", the Tech 21 PE60, I found that I preferred having a KPA Cab profile enabled. Note -- As the PE60 is a powered speaker, I was connecting my powered KPA using the Monitor Output jack, with the built-in poweramp turned off. In any case, I found that the speaker in the PE60 (Celestion Seventy/80) sounded best with (believe it or not) a Cab Profile from TAF, based on a 1x15" Ampeg SVT 450 Bass Cabinet.
So, there are no hard and fast rules. At the end of the day, you will find out what works best with your unique set-up. Again, 99% of the time you probably will want to have your KPA's Cab Module off (when connecting to a traditional guitar cabinet). But every once in awhile, you may find a sweet combination of a KPA amp profile and your connected cabinet which benefits from having a particular Cab enabled.
Cheers,
John