I need more volume on stage.
I think I am missing the boost power of my tube amps in the past.
When doing rehearsal with band, I feel to have not enough headroom and very compressed sound.
I've included both quotes because I think it might be helpful to better understand what you're missing in rehearsal. In particular, your comment about not enough headroom and compressed sound makes me think the problem you're trying to solve isn't necessarily just the raw volume db measurement.
First, a little context. I have a powered toaster and prior to buying an FRFR, I ran into a sealed cab with a single Celestian V30 speaker. I could hit 105 db without breaking a sweat, and that's just where I stopped turning it up because even as a rock guy, that's starting to get a bit hard on the ears. So, I know the power amp will deliver the volume, but that may not be the entire story...
I play classic rock, so more often than not the tones I'm going for are your typical Marshall on 11 kind of thing. When I'm pushing the speaker with higher volume, if there's some compression that's not a bad thing for my tone. Your user name is Chicken Picker, which would lead me to believe you play in a country band and thus have more need for clean and snappy tones with distinct attacks / transients.
If you start getting compression with those kinds of tones, you're obviously going to feel it. A clean, high headroom sound at loud volumes will pierce your ears (if they're not pierced already) and can at times be painful because of the uncompressed transients. A rock distortion tone at the same db level isn't going to feel as loud as a completely clean tone at the same volume because of this.
I mention all of this to offer another possibility for you to look into. It sounds to me like at rehearsal volume you're not hearing the kind of clean, twanky / spiky / sharp transients that you want in your tone, and you instinctively interpret that compressed sound as "not loud enough." Even if you fire up a db meter and it says it's X dbs and that's mega-loud, it doesn't really matter. All that matters is that you're not feeling the tone you want to feel.
With that in mind, and because I'm pretty confident that the power amp in the Kemper is capable of delivering the raw db levels, you might try skinning this cat from a different direction. If you start with the working hypothesis that the power amp is capable of delivering the volume, that will then lead you to investigate other solutions. Consequently, the next step would be to search for profiles that deliver what you're looking for at volume.
So, while not invalidating the question you've asked here, you might start another thread mentioning the kinds of bands / songs you play to give people a common point of reference, include the fact that a lot of profiles feel compressed at volume, and ask the guys what profiles they use to get the kind of tone you're looking for at rehearsal / gig level. These are a great bunch of guys and I think you'll get a lot of worthwhile suggestions that may, in fact, be the actual solution to the problem you're experiencing. At the risk of overstating the obvious, with a Kemper the profile is everything.
For the record, I couldn't pick a chicken out of a police lineup, so I'm personally pretty useless to you in this regard. However, there are a lot of guys here and I'm confident that many of them need high headroom, uncompressed tones at high volume, so they can recommend some profiles that might get you closer to what you're wanting to hear.
Hope this helps!