First at all, thanks for answering Ingolf.
I understand your point but then I'm seriously disappointed because one of the main reasons why I made up my mind to go Kemper was leaving behind head and 4x12 cab and being able to plug and play at ANY rehearsal place, jam or gig with ANY mixing desk.
And going further, I had the same reasoning about playing through FOH, but probably, according to your words, I was wrong.
So it will not work depending on the speakers of the mixing desk or foh?
Truly disapointing... or maybe is there some point I'm missing? Again, thanks for your support
Ofcourse, no 2 PA speakers are the same. They all aim to have a flat response, but there is a difference between a 500 euro studio monitor which doesnt go nearly as loud as a PA speaker and can put all it's effort in giving good sound, and a 500 euro behringer speaker, which has to go loud first, or a 100.000 euro (yes, a six digit figure!) Adamson line array, which can do both flawless on 50.000 people-festivals.... Of course, all shades of grey in between... I am still astonished by how many bands put their singers through cheap crap speakers and expect this to sound pleasant. Same with the Kemper.... Any decent soundtech will cringe at the idea of mixing through a sub 3000 euro PA... But bands don't seem to care....
Now, before you think that's a turnoff to the Kemper, you forgot one important thing: If you go with a real cab, in any room above 50 people your soundtech will likely want to mic your cab and put that signal through the same speaker you would be putting your Kemper through. Only difference is, you don't hear it, because you stand in front of your trusted cab... But it may or may not be a massacre out there. Not only because of a mediocre PA, but also because of mic spill and bad mic placement, and especially those last 2 are ruled out with the Kemper....
Thing to learn here, in any case, Kemper or real cab/amp: if you want to sound good as a band, don't perform through mediocre PA's. No Behringer, even Mackie is questionable.... You don't have to put Adamson on your rider, but "respected A brand in working order" is regarded as a standard sentence in a rider of any quality band.... If you don't stand by this, don't expect to sound good, even with a real amp, it's not because you don't hear it it isnt there....
The next question I hear from a lot of newcomers in the digital amp sim world, well, how do I tweak my presets with so many speakers out there? Well, simple, with a speaker that sounds as neutral/flat as possible: a quality set of headphones, or a quality studio monitor (not KRK G3, far from neutral, neumann would be a better choice). And maybe ask your local PA company if you can play sometimes through their PA/line array, just between the PA being set up and the crowd arriving: stand beside FOH desk, plug Kemper in desk, go wild. Maybe judge that speaker/system first by playing you favorite music through it, and adjust your guitar sound accordingly (just like a studio engineer does with hit studio monitors, he first has to learn their sound before he can craft a neutral mix through them....).... And if it then sounds crap through that Behringer speaker in your rehearsal room, well, probably your favorite recorded song will sound crap too, and then thats because that Behringer speaker is crap, not because the Kemper is....
PS: don't forget the room.... The room can make even a top notch line array sound mediocre. Or your trusted guitar cab... Or even have a spot that the cab sounds good, while 1 meter further it sounds crap....
Open air is the best because it has the least reflections....