I was looking at the Power on/off issue too, there is a newer TS-590 CAT guide that speaks to that.
It was version 4 of the CAT guide from Kenwood, as I recall.
That guide mentioned that the TS-590 can be put into 2 different modes of Standby, and that it is never fully turned off.
It leaves the USB ports and processor in low power mode but able to receive a CAT command to turn on.
Then the CAT power on command needs to be "padded" with extra characters for time to "awaken" the processor and then the Power ON command will work when sent.
73 - Mark - K8MHW
'A RigPi Enthusiast!' - I am not otherwise affiliated with MFJ or RigPi