If you look at the BrightSign object reference manual, you'll find details about the Serial Object that's used to send and receive information over the serial port. There's no fixed set of commands the unit will respond to. You can send any command. Raid full movie hd. Assuming your PC has a RS232-port (last time I used it was with a 300 bps modem, back in 1992 or so, and I don't have that PC any more) use.
B) use a telnet programm (e.g. Putty) and try to send the commands from there to the IP address/port of the KISSBOX. Use UDP to send the data! Probably you do not need to add the CR/LF (x0D) when using Putty since pressing the Enter key just adds this by itself.
How To Send Serial Commands
T he AT-UHD-CLSO-824 acts as a RS232 (serial) hub by allowing you to connect one input to the “Master RS232” port and then route commands to any of the 15 output zones on this unit. The first 10 zones correspond to their respective RS232 outputs. This is designed for control of local sources. The other 5 RS232 outputs are found on the HDBaseT inputs and outputs. RS232 zones 11-13 are tied to HDBaseT inputs 1-3 while RS232 zones 14-15 are tied to the HDBaseT outputs.