Some Radeons do support dual head, so 1 extra Voodoo might do the trick.

I'm not sure if any cards supported on the X5000 have that enabled (might be limited to a few genuine Apple cards).
Otherwise you would need to hunt something down what was supported by GRex, so Permedia would be a good guess.

Or you use 2 cards and get the 3rd monitor with VNC and a rPi (or similar) driving it.

As for the picture, it is not only clearly rendered but would still be fake if it wasn't as MorphOS does not support pivot (the outside monitors are at 90°) or maybe you could "fix" that with 2 VNC sessions.