To check the firmware version of the Mixer Amp and microphones connected to it, serial commands can be sent to the RS-232 port using a Vaddio Loader software. Typing 5202 followed by the port number (00 for mic 1, 01 for mic 2) will return the microphone's firmware version. The document also lists available commands for getting and setting various status and control parameters of the Mixer Amp such as mute, volume, gain, and enabling serial echo. Error responses are provided if an unknown command or invalid argument is given.