This device is basically a footswitch simulator. It will accept MIDI Program change messages and switch the amp channels/functions accordingly. It'll be connected to the amp by the footswitch cable using DIN7 connectors. MIDI won't be the only way of controlling the amp as there'll be six switches included (as on original Mesa footswitch) to change the amp settings without having to send MIDI messages to it.
The project is inspired by a great video series "MIDI for the Arduino" by Notes and Volts on youtube, as well as "Happyswitch" project, which does a similar thing for Mesa Rectifier series amps. Both projects are linked below.