So my possibilities are at the moment:
- a dedicated headphone amp for my old interface and recording the kemper through the preamps (cheapest option, 50-150 euro)
- a new interface with SPDIF and a good headphone out (200-500 euro?)
A 3rd option:
Plug one set of your audio interface's outputs into the Kemper. Then you can monitor your DAW and your guitar from the Kemper's headphone output, and get that killer sound. I use this mostly. (for the reasons you describe) But can also just plug the headphones into the audio interface, or use monitors at any time. In the RIG menu, there is a panorama control, so you can pan the guitar signal to hear the daw playback easier when tracking.
I forget right now what they're called, think it's alt. input and return input you use for the cables.