How to do a plain DI signal out of the kemper?

Direct Output for DI out, and set Direct Output = Git Analog on page 1/9 of the Output settings pages.

As the Texan said, you can use the Direct Out or you could just turn off the amp and cab sections of a rig and have Direct acoustic but still have FX like compression, EQ, delay and reverb available to sweeten things if required.