Ok, I asked you these questions because:
1. If you record the DI track through S/PDIF, you'll get a signal called "Git Studio" on the left channel of S/PDIF. This signal is your guitar going through AD conversion PLUS it's affected by the Clean Sens setting (one of many reasons I never ever mess around with any of the Sens settings. They will always sit at default 0.0, all of them)
2. If you are on firmware 8.7.1 or 8.7.2, there were issues with S/PDIF in both of them. Just today Kemper released a new (public beta) firmware that is supposed to fix these issues (8.7.3) that might have caused you headaches.
3. Whenever I record a DI track through S/PDIF, I always have the SPDIF output turned down to -1.0dB in the Profiler Output settings because this way I prevent inter-sample clipping. A setting of -0.3dB might already do the trick but I rather play it safe.
When I reamp through S/PDIF, I basically boost the signal by the corresponding amount in my audio interface's DSP mixer to be back where it was.
4. Just to be sure, you record the DI track into a mono track, right? And when you send the DI track to your interface's left S/PDIF channel to reamp, this also is a mono bus in your interface's DSP mixer? I'm just asking this because I've seen people struggle with the effects of panning laws and sudden / unexpected 3dB level bumps out of "nowhere".