Here's a quick video of energyXT loading the VST file that connects to Beat707 via the USB cable. No MIDI devices were used for this example, but Beat707 is sending regular MIDI data via the Virtual Serial connected thanks to the FDI chip. Resuming: no hardware or software changes. (at least no big software changes)
During the Beat707 startup, it starts at 57600bps, sends 4 bytes of a code to the serial output, waits 1 second, and if nothing is received, it re-starts the serial port at 31250bps and enables the midi connection.
The VST file checks all Serial ports, for each port, it waits 2 seconds, so the Arduino has time to reboot and send that 4 bytes of code above, and if the code the VST reads is ok, it sends an OK message back so the Arduino goes to USB mode. After that, they "talk" to each other. ;-)