If you set parallel path, you can add two FX to the A and B slots on the Kemper, including OD/DS stomp boxes. These two slots will be directly output to the direct output with just those stack sounds. Your main signal will be with stack using the remaining six slots.
Is that what you are trying to achieve?
the parallel path does not send the signal to the direct output but instead forwards the signal after Stomp B to the master output bypassing stomp C,D,the Amp Stack and the effects. The only way to achieve what the OP is after is by assigning a mono loop to stomp B.