Having owned both the KPA and the AX8, I have to say it's a draw. Both sound amazing. But for me it's a matter of which annoys you less.
For "feels like an amp"... the edge goes to the Kemper. Barely.
For amp tones... it's a draw for me. I've said for years, the Kemper soars for Fender/Marshall tones, but FAS can do a dead-on Mesa Boogie much better. FAS has an amazing model of the CA Tucana but then there's @rmpachecos AC20 KPA profile. When I got the AX8, the first thing I tried to do was dial in that AC20 to sound like the KPA profile. To my surprise I was able to get 99% there diving into the power amp compression parameters. FAS can do a stellar Plexi in 30 seconds... but Nick's PT20 profiles are hard to beat. With FAS products, the amp controls behave exactly as on the amp, whereas the KPA has the same tone stack for every profile. I prefer the KPA way, but a lot of people like the controls to behave like they do on the real amps because they have experience with those amps. If you let yourself get sucked into all the advanced amp parameters on the FAS units, you'll probably run home to the simplicity of the KPA.
In the end, having come back to the KPA after having owned the AX8, I can honestly say the Kemper doesn't sound notably better in very many instances. It really depends on how fast you can narrow down the right KPA profile, or with FAS, dial in the amp and find the right IR. Different sides of the same coin in my book.
For effects... if you're a bread and butter boost/reverb/delay/chorus kind of guy, the KPA is fine. But honestly, the depth and breadth of FAS's FX implementation is truly astonishing. It's not. even. close.
For remote control & MIDI... if you buy the remotes from KPA or FAS, you're fine. Dialing in 3rd party remotes is easier with FAS, considering they actually <cough, cough> publish their current MIDI implementation.
Rereading your OP just now, I'd try the AF3, since you already know the KPA. If you're completely thrown for a loop, you have 15 days to return it, or ebay it to Europe for a profit.