First draft of code written, ready to test tomorrow:

I have taken some working test code I had written for the Pro Micro and splits out its functions; the pro micro now becomes an i2c master, converting receive data into MIDI commands, and the slave device will focus on reading pads and sending values back to the master. In this example I'll be putting the slave code onto a Mega, giving 16 analog inputs (enough for 8 pads).

If this works I'll be a happy man, as it'll allow me to easily add more slaves to give me the number of analog inputs needed, or allow me to use clusters of smaller boards, such as Nanos.