I had few more hours to play with radios so I also found NaP3 software by Pete F5VNB.
It is based on earlier versions of PowerSDR/IF and PowerSDR* 2.1.4.
NaP3 has integration with Elecraft KX3 CAT - see instructions here: http://www.telepostinc.com/NaP3.html#Setup
Works well except I have some noise +/- 2.9 kHz around center frequency, probably coming from RX I/Q cable connected to PC soundcard. Setting "Global IF Frequency Offset (Hz)" in "IF Frequencies" tab to 3500 Hz moves the noise so that I does not impact listening.
If you have Elecraft KX3 and a Windows PC with audio card NaP3 is well worth trying out. You get a free SDR with 96 KHz wide panadapter / waterfall display by investing 10 -20 minutes to configure it.