The alpha version used a custom built button grid that was equivalent to all the buttons from two regular joypads.
The original Mega Drive visuals matched the 5 x 4 button layout of that grid as shown below.
Though still in development, I risked playing live with the alpha version using the dual joypad button grid - it was a lot of fun, though the software was still a little buggy and unstable. Here's a video clip courtesy of xspheric from the first ever live performance using the software. Everything except the main melody being played on the keyboard is from VGX Live. You might not notice that VGX Live actually crashes at the end!