I kinda get the, "I own the vintage amp" - but they tend to be unreliable as they age... and for some amps, things like the original transformers and certain other components are hard to source and replace like for like. They'd be better doing their thing in the studio without having to suffer the ordeal of having a touring life.
As for Angus' hearing... well, if I was a betting man... I would put money on him not having a clean sheet when it came to passing an audio test.
Having said that, I do recall him being really particular about using a vintage wireless due to the impact that it had on his tone. Hang on... Yes, the Schaffer wireless. And check here - https://solodallas.com/the-schaffer-replica - somebody makes a pedal to impact the tone in the same way as the wireless system.
Anyway... to the Kemper... You can do better than that. When you profile, you profile the sum of the x number of amps. That will give you one profile that models the sum of those x number of amps. The only reasons for having two Kempers would be for redundancy.
Then if he wants stage sound, it would be PA cabs housed in a Marshall cab... with a SM57 with a cable plugged into it just to keep the charade going.
Of course, it could be all nonsense... I mean, take Steve Winwood, somebody who has considerable hearing loss and what he has to say about his Kemper.
"Kemper has revolutionized my thinking on guitar amplification. The sounds are completely true to life, matching faultlessly the models they are profiling, and unlike other amplifiers it is not subject to mic placement or level.
A phenomenal achievement!"
- is that a strong endorsement? Its not far from asking Stevie Wonder what he thinks of the new paintjob on his piano.