Uhm do I need to use interface at all? From the posts above what I get it is possible to use simple input, but is interface needed (DI BOx is not needed, right)
Can I just run the signal directly from my pc to the input on the back?(Doesnt it have different impedance than the input in the front already?)
I tested Focusrite Scarlett and Steinberg UR44- both sounded a little bit different with my monitors, but not really better than the output from my PC. I even have SPDIF output on the motherboard, so not sure if there is any advantage, maybe I am missing something.
Sure, you could reamp with your PC motherboard output, but whether you can then route the resultant audio to your speakers. etc, I am not sure.
This is because I've never tried doing this with a built-in audio card, my guess is that you will only be able to route the same signal to all outputs, rather than different signals to different outputs. This would mean the DI signal that you are feeding the Kemper is fed to all other outputs. Again, this is just a guess.
The advantage of having a dedicated interface is that you'll be able to achieve more complex routing and lower latency because you are taking this processing task off your motherboard and will have dedicated ASIO drivers.