Content provided by Michael, VA3MW
The SonOff 4 Channel Pro relay which is available on Amazon World Wide and at a reasonable price is a good option for booting a FLEX-6000 remotely.
There seems to be a few versions of this switch, but the one I tested had 4 SPDT Switches
The device is powered by 9-24V DC or 90-260VAC. The one I have requires a Canon connector for the 12V I used, but others may have a quick connect terminal. You should have no issue powering it from a Wall Cube that you already have in a junk box or your station's DC power supply.
The one I tested was the V2 and I was able to use it to connect to the Remote RCA (REM ON) connector on the back of the radio for soft power up and power down.
I also used a 2nd contact for PTT should you ever need to do a remote SmartLink registration.
They make many versions of this, but you want the one that shows the NO/NC contacts as on the bottom of the case.
It does require that you use the eWeLink app on your SmartPhone (I only tested on iOS). https://www.ewelink.cc/en/
I did a very basic schematic that you can reference. R1 turns the radio ON and OFF and R4 would do a 1 second PTT to the radio. You need to set R4 for 'inching' and you do that in the eWelink application.
I found that on the one I had, I had to open the box and change some dip switches.
S6 had to be set to 1 and K5 had to be set to all 1's (closest to the relays).