Maybe my settings will be useful to someone.
I have made many attempts to set the FT8 emission. All descriptions I found on the internet regarding this TRX are based on the inclusion of USB VOX. However, I wanted to start transmission via PTT and not USB VOX. Finally, after many attempts, I was able to set parameters so that the transmission would take place via PTT.
Connection to the computer only via a USB cable. System macOS Mojave.
Before connecting the cable, of course, you must install a USB driver.
Another USB driver is intended for the macOS system, as shown by the default (Windows only) Kenwood website. It's easy to find.
Settings of the TS-590SG menu:
No. DESCRIPTION
68 USB Port Baudrate 115200
69 Audio Input Line selection for data communications USB
70 Audio source of SEND/PTT transmission for data mode REAR
71 Audio level USB INPUT for data communications 3
72 Audio level USB OUTPUT for data communications 3
76 VOX OPERATION WITH DATA INPUT OFF
78 USB VOX GAIN 0
Below images of the RUMLOGNG and WJSTX settings.