The Matrix GT800FX is a really popular SS poweramp and many Axe-fx users rave about it.
Matrix are soon releasing a smaller poweramp (GM50) that seem to fit nicely inside the KPA.
No clue how it would be seated in there though, so maybe not possible...
"Class A/B Mosfet, equivalent power of a 50watt tube amp, weighs less than 2kg. can be installed in the back of a guitar cabinet".
See info:
https://www.facebook.com/MatrixAmplification
youtube video link
(how can yt videos be played directly in threads here?)
http://www.youtube.com/watch?f…er_embedded&v=5WNMuV4-fJY