Peavey Ultra Plus
I'll counter there is no amp/preamp that can be captured more accurately on a recording than it can be profiled.
I may not be able to get it right, someone else might not, but that's based on the profiler's inventory or microphones, ability to place them, as well as ability to physically place the speaker in a room that is well chosen for the task.
And, if "the box that must not be named" can be successfully profiled over and over again, getting any other "ampless" processor right would largely be matter of level matching and refining.
I'll counter there is no amp/preamp that can be captured more accurately on a recording than it can be profiled.
I may not be able to get it right, someone else might not, but that's based on the profiler's inventory or microphones, ability to place them, as well as ability to physically place the speaker in a room that is well chosen for the task.
And, if "the box that must not be named" can be successfully profiled over and over again, getting any other "ampless" processor right would largely be matter of level matching and refining.
I would've said that 2 weeks ago, but after trying on three different days with three different instruments in three places, I can't get the Sansamp RBI to sound like anything but shit when profiled by the KPA.
Fender Super Sonic... somehow I couldn't get it profiled accurately.
In the process of creating the tonematches i did with ozone last year, i came across a few sounds that the KPA couldn´t capture though the ozone tonematch worked fine. What´s interesting about this is the fact that all those sounds were extremely scooped, like Pantera´s "vulgar display of power", life of agony´s "river runs red" or fear factory´s "demanufacture". The sound was close, but not as scooped as for a 100% match. You could get the remaining few percents with the studio EQ though. Nonetheless i had the impression that the KPA doesn´t like those extreme scoops.
That's the joy of absolute statements. They absolutely can be refuted 
Perhaps the extreme scoop exceeds the maximum Frequency cut amounts designed in the Kemper.
This combo. Has been impossible and I've tried with every possible mic... Has a really warm sound.
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That metal grille cloth is the problem. It produces a comb filter effect that time delays partial harmonics. Even though the Kemper does its best to compensate for that sort of thing, it is inevitable that a profile of that will sound metallic and boxy.
Tried to profile my usual bass recording rig - di bass with eq scooping low mids mixed with high pass filtered marshall jcm 800 for the dirt - mixed to one track on a desk into kemper - miserable fail...sounded way off. But what the heck, it rules 95% of the time. But I wonder what makes a rig unprofileable?
This combo. Has been impossible and I've tried with every possible mic... Has a really warm sound.
You put the mike on the cold side. One cannot see any hole for miking!
You have to put the mikes on the other side which is hotter, there you get the warm sound. 
I tried to profile an Ampeg SVT-CL with an 8x10" cab and failed miserably.
Tried to profile my usual bass recording rig - di bass with eq scooping low mids mixed with high pass filtered marshall jcm 800 for the dirt - mixed to one track on a desk into kemper - miserable fail...sounded way off. But what the heck, it rules 95% of the time. But I wonder what makes a rig unprofileable?
That is a layered setup. KPA can't do things like that as you are mixing a clean and dirty tone layered using a crossover.
