Do we know for certain, that the amp part of DI and merged profiles are 100% the same? What really happens, when the merge button is used? Can we be sure the amp part is 100% unaffected?
Great question! This depends on the DI and Studio Profiles used to create the Merged Profile. The DI Profile needs to be the exact same as the Studio Profile, but without the Cab in the Profile. If the DI Profile is done after the Studio profile, and done with the same settings, the Merged Profile's amp section should be the exact same as in the DI profile and the Studio Profile.
Of course, this is all in theory and the outcome comes down to the way the process is executed. When you press the "Merge Cabinet" button, Kemper compares the DI profile to the Studio profile that the Cab section was taken from, and subtracts the DI profile from the Studio Profile to get an accurate assessment of where the Amp section ends and Cab begins. Otherwise, CabDriver is just guessing where the Amp ends and Cab begins. So "Merging" a Studio Profile's Cab section from a different profile set or something, can change the amp section (in certain situations).
And of course, you can always test these things for yourself, as I try to do when I'm curious about something such as this You can go through the process of correctly making a Merged Profile, and before saving, you can turn the Profile's Cab section off and run the Kemper into a real Cab, and then toggle "Merge Cabinet" on and off while keeping the profiles cab section turned off to see if the Amp section changes when being "Merged". This is how I have tested this out with various Profile sets (its important to use Studio and DI Profiles made in the same session or equal to each other for accuracy) and I found the outcome varies and really depends on the DI and Studio Profiles, and whether or not they were close enough to the same to begin with. That's why for the most accurate results, it's recommended to use a DI and Studio Profile made with the same Amp settings or from the same session Profiling session.
Another question. I know for sure, some commercial profilers sell "Merged" profiles, that in reality are only direct profiles with copied cabs from earlier profiling sessions (or the same cab copied to different DI). If this cabs are maybe just copied from studio profiles, cab driver is still active on this rigs. Is the amp part affected too in this case (cab driver guessing again)?
In the situation you're talking about, it depends on whether or not the Cab from a different Studio Profile from a previous session has been "Merged" or not with the DI Profile (whether or not "Merge Cabinet" was pressed). It's possible to just use Cab section from a Studio profile with a DI profile and not merged the cabinet. If the Cab section isn't "merged" then the algorithm that compares the Studio and DI Profile to find the Amp and Cab seperation isn't engaged. And if it isn't engaged, then the Amp section of the profile should remain unchanged.
Without engaging "Merge Cabinet", it's just like layering a cab section after the DI Profile and it won't change the Amp section. But once you "merge" the cab section, that's when the Amp section can be affected by the "Merge Cabinet" function depending on the DI and Studio Profiles used to make the Merged Profile. If done correctly (by using equal DI and Studio Profile), the Amp section of the Profile should be the same as before. But like I said before, In practice there are a lot of variables and the outcomes vary quite a bit.
I've actually experimented a lot with "merging" cabs and making Merged Profiles out of various combos of DI Profiles and Cabs from Studio Profiles that I've saved as Presets. Sometimes using "Merge Cabinet" with Profiles from different sources can yield really good results depending on your preferences. I actually posted a thread about it a while back called - "Revelation for Merge Cabinet" or something like that. It explains some of the results I've gotten when experimenting to give some insight for people wondering more about the "merge cabinet" function.
But regardless, you can test all of these things yourself to find out the effects of making Merged Profiles using different methods and that should at least give you some perspective on the questions you asked, as well as helping you form your preferences as far as using different types of Profiles for different situations. It can't hurt to try some of this stuff for yourself It definitely helped me get a better understanding of using the "Merge Cabinet" button and helped me gain a better understanding of the different types of Profiles and making Merged Profiles And if anything, it'll at least give you the opportunity to find the answers to your questions first-hand, so you don't have to just take my word for it
All the info given in this reply is based on research, experiences, and info from other Kemper users. But I'm not always right and there's probably info I'm missing, or info I'm not getting 100% right lol. But I'm sharing in hopes that some of it might help answer some of your questions, or encourage you to try these things to find out first-hand and get answers that you can be confident about