Brian, your software version is dated 12/31/1991. There have been a LOT of changes/additions to the Milltronics Centurion control since then. The older software would probably have problems running the newer code but you can try to verify the program. If it verifies, it should run.
You will have to trace the wiring from solenoid connected to the brake air cylinder to determine which output pin controls it. Then you can look at the appropriate Display-Diagnostic screen to see if the HEX files turns it on with an M5 command.
Xout2 is the Mist output so you can use that output to activate a 24vdc coil solenoid directly by connecting one side of the coil to TB12(24vdc) and the other side to the #2 pin on the X output plug. The outputs turn on/off the 0vdc signal of the 24vdc power.
You can control any of the un-used outputs. For example, to turn on the Xout10, you use a SETX10 command, and to turn it off, use a CLRX10 command.
You can create your own 'Custom M and G Codes' to do many things by controlling outputs and monitoring inputs.