Just connect it in analog to you interface and record at whatever rate you want...where is the problem? The balanced output of the Kemper is a lot better then most of studio amp/cab/mic I know...
The problem (as has been covered elsewhere in this and other threads before) is that it adds extra levels of conversion that shouldn't be necessary on a digital device and more latency. In addition SPDIF allows you to use your own convertors for bringing the guitar into the Kemper int he first place which allows you to get a higher quality signal in, and finally it allows you to record both a dry guitar track and the distorted track at once for later tweaking and re-amping, and it allows you to do that with full stereo from the KPA rather than dual mono (one dry the other with effects).
SPDIF is a great standard, it's on the Kemper for a reason, why have it but then cripple it to the point that you have to use the analog outs instead?