I have yet to profile an amp using more than one mic. For now I only used a SM57 and tube mic preamp into console into Kemper.
I do not really understand the concept of mixing different mics during a profiling process.
Mixing microphones whilst recording is studio routine, it is used to get a different sound, sort of used to EQ the signal from the cabinet by using different mics and mixing the different frequency responses of the mics.
This might be IMHO a bit too much info for the Kemper. I assume the Kemper "records" the frequency response of the whole system: Amp, cabinet, mic, mic preamp, mixer. So if there are two mics mixed, the Kemper calculates a mix of the freq response of those two mics (phase cancellations and all). Which of course might be something very different from what we hear in real life when mixing two mics.
I tend to think that profiling should be rather explored using a single mic and maybe different types of mics.
I've had good results using two mics to profile: Shure SM57 and Shure SM86. I run them into a Mackie mixer then into the KPA. It just seemed to me that mixing different tonal characteristics would result in a truer sound, but I'm sure no expert!