My guess is that it comes down to the bottom line--Kemper probably had a price point that they wanted to meet, and a compromise had to occur somewhere--so perhaps there was a hardware cost-cutting measure, or they just felt like the current processor was up to the task.
When Line 6 made the POD X3--which had lots of aliasing--that unit had the SHARC ADSP-21369 at 266 MHz (KSZ-1A), 1.6 GFLOPS DSP, and when they put out the POD HD, which had no noticeable aliasing, that unit had the SHARC ADSP-21369 at 333 MHz (KSZ-2A), 2.4 GFLOPS DSP.
I imagine there was plenty of code updating, but without that faster processor, I doubt L6 could have eliminated the aliasing.
The Axe-Fx II has [2] ADSP-TS201S: 500/600 MHZ TIGERSHARC PROCESSORS with 24 MBIT On-chip EMBEDDED DRAM. Though I think the KPA is superior in most ways, the Axe-Fx II likely has more horsepower. I peaked inside the KPA and saw one main DSP with no name on it, so who knows if there is enough power there to faithfully produce the kind of resolution we would expect.
Kemper beats Fractal Audio in value, but I would have paid more to have the ultimate KPA with no compromises--that's assuming they did compromise, hell, maybe they will correct this in the next firmware update, then we can go back to making music and stop speculating.
Kemper, may we please have some specs? If you don't give it to us, we love you anyway... but throw us a bone.