I think you are always going to get substandard tone with the Kemper when using guitar speakers. Trying to mix FRFR and guitar speakers is, from a tone standpoint, probably the most challenging of all possible scenarios.
Here's another thing - by micing up a cab for taking a profile, you make the cab an integral part of the tone profile. That's great if you are running FRFR. But if you are using a guitar cab in your rig, you run into problems. The reality with a Kemper is that it's not really possible to perfectly take out the cab portion of a profile. If you turn the cab portion off, it has to try to cut out a part of the original profile. The Kemper does its best, but that's a really hard thing to accomplish. It's an approximation, but the end result reveals its limitations.
When I gigged my Axe-FX (2008-2011, on and off), I was happy using a Mesa 2:90 and Recto 4x12 for gigs. But that's because when creating Axe modeling patches, the cab was added after the amp block was complete. As as separate part of the patch, it was easy to simply delete it. Trying to take the cab out after profiling on a KPA is tough (unless you are profiling directly out of the head). The Kemper tries to approximate it, but it's not nearly as good as going FRFR.
When I first got my Kemper (Feb 2012), I tried to run the same rig, thinking the tube power amp would 'warm up' the digital signal. But the KPA isn't another flavor of the Axe. It doesn't work the same way, and doesn't need its tones to be warmed up.
There really isn't a better way to run a KPA than with a truly flat response speaker. What kind of speaker is your FRFR? Some are great, and some are not as great (because so many monitors are not really a flat response). If it is at all possible, I think you'd be MUCH happier running FRFR for your wet and dry speakers.
Although I prefer other mics, the 57 isn't a terrible mic. It does tend to add mids, and back in the day before amps were voiced with more mids, it was the best mic available for guitar cabs. But amps built after the 70s usually don't need that mid boost, and the added mids of the 57 aren't necessary, imo. However, lowering the mids and slightly bumping the lows in the Kemper EQ often counteracts a 57's effect.