how to insert Hardware Pedals when Re-amping with Spdif?

Put the pedal in in the Kemper FX Loop. Place a Loop early in the chain say Stomp A.

I think you can run your DI out from DAW thru your interface Line out in and into the kemper input then place a with hard pedal in front. If you do reamping like this often, try putting a looper in front of kemper and add hard pedals to that after you record the loop.