The concept: Stereo sound has 2 channels, Left and Right. Mid and Side simply means:
MID - the sound that is common between Left and Right
SIDE - the sound that is different from Left to Right, and Right to left.
They are separated in Satellite to reduce bass frequencies in the Side.
To separate the two, take the input and make it mono. In a separate input, take the stereo signal and invert it. Connect the inverted stereo and the mono signal to an amplifier to isolate the Side. Take sound directly out of the mono output to get Mid.
Also worth noting that the Simple Mid/Side switch is just an optimization of what TB was using before (to reduce filesize), although I made it from scratch