Successfully installed on a KX2.  Make sure you change the RS232 speed to something less than the default used by the utility (38400).  I used 9600 in the setup of the KX2 under RS232.  It works fine.   I plan to do it next on my KX3.   The KPA500 is not bothered by the TX being out of band.  Test it on a dummy load as it will not be resonant on your amateur antenna otherwise without using an impedance matcher.