Real guitar feedback needs speakers, volume and proximity.. but if the old school earplug way isnt your bag (it is the Kemper forum afterall!) then imo,
- The current Kemper FW has nothing on board that can simulate feedback. This makes me very sad.
- Convinving speakerless feedback can be done with the Digitech Freqout. Just dont expect it to be fawless all the time. It does add a very cool live feel if set subtly and tastefully -but- is still no substitute if you're a 10 second intro feedback kinda guy. When your natural string sustain dies, the feedback effect gets very confused and the illusion is wrecked. That's the trade off. For me though, the Freqout is amazing for adding spice to IEM live solos and more intense sections.
Atm it's the best we have unless you want to stand infront a speaker and blast yourself with... yourself. .