Compatibility of equipment when adding a dac?

And I also believe that the Marantz only outputs PCM in its digital out. This means it should be compatible with any DAC, just not DSD. I am not familiar with this DAC, but assume it's standard in terms of capability.

I believe only DSD capable DACs can decode SACD...

Have you looked up the ways that the Krell imports digital data (music) and the ways the Marantz exports digital? I would guess that there is a high probability that they Krell will have one or more digital inputs that the Marantz uses to output, but just guessing.