This is what I don‘t understand.
I cannot see a way how you would vary the volume of a (significantly) distorted amp by swapping the OD, or changing the volume of the OD.
The distortion of the amp would compress (sic!) the volume differences, but response with a different level of distortion.
My setup at home is made to use the Aux Input with my PC and be able to listen back to tracks and youtube lessons on the same headphones as I play thru the Kemper. This makes impossible to use the effects loop. For my initial test I went and disconnected everything and enabled the effects loop. I did the testing and found that for the clean (gain at 0 in the amp) and until a significant amount of gain in the amp, the Maxon had clearly a lot more volume than the Kemper Drive. I´m not talking here in super high gain where there is no room for more volume and any amp would just change the tone, compress and change the quality of the distortion, but in the low range of distorted amps where many people use their overdrives to get a boost for a lead part for example. Now based on your recommendation I went back to my usual setting with the effects loop disabled. So I am not able to try it again to report back with the exact gain figures until I have some spare time to do a new test on the effects loop.
If someone can do a similar test with a similar Tube Screamer pedal I would rather keep my testing on the suggested setting of connecting the Maxon Overdrive in front of the Kemper.
Last night I tried again in this setting with the pedal in front of the amp. Right now I can't report any conclusions. This way it all depends completely on the Clean Sense setting that you have.
Using the +6dB setting that you ckemper suggested the volume difference at maximum settings for a Profile that has gain at 4.4 value between the Maxon and the Kemper Drive is huge.
Are you sure you didn't mean -6 dB?
I think I still have a lot to learn about Clean Sense and the way to take complete advantage of it.
My way of thinking would be that Clean Sense is made to adapt to different guitars, but as soon as I put a pedal in front and rise the volume then I get a different response like I would with a higher output guitar. And that was what led me to think that probably the way of making things even was to use the overdrive pedal in an "intended for this use" Distortion Loop. With the results I already told.
Right now I would not know what settings use to try and make a list of presets for the community to use and get similar results with their setups.