Its true a Matrox Mystique with rainbow runner daughter board was pretty hot stuff in.. 1996-1997?
I can tell you I myself had a couple voodoo 2 cards running in SLI mode. Yes they run in tandom with you 2d card, but I ran those until about 2001, They never let me down. A pci voodoo 3 card is also a good choice for 98 era games.
I am not sure why you'd put a 3d accelerator in a machine with a first gen Pentium.
Why wouldn't you?
Many hardware accelerated games required MMX at least
(is a P233-MMX, a first gen? that's another question...), and any of them would benefit greatly from the FPU in the p6+.