Burkhard - users may wish to record their KPA using the USB/SPDIF no matter what the configuration. Having options to go out to another stereo effects unit - or a whole chain of them - and then come back to the KPA and use the Kemper stereo fx after external modulation effects (for example) and then exit in the digital domain via USB or SPDIF to your DAW.
Consider also the possibility of not wasting the KPA's stereo FX slots with [send/return units]. Allow the user to retain all 4 post amp section slots for the internal effects and insert a [stereo send/return] circuit in between the slots at a location chosen by the user from a menu.
We do this with the space effect on the output - an effect is applied in this case but no wasted slot - excellent idea it was too.