Hi! I’m new here, but I can advise you to read this page
[Firmware Upgrade 4.2.9326.26]
and download a description of the UART commands. To obtain information about the active source, send a STA; request, and read in the response line which input is active. RX TX pins are located on the connector with outputs for LEDs and analog keyboard. Logic levels 3.3v. I was able to control the board and receive feedback from it using arduino.
ALSO You can send “SRC;” request and receive answer like “SRC:NET”