Nice combination you have there, I also have a Matrox G400 (regular 32M DH) and Samsung 950P, looks great! I bought a BNC cable and hooked it up, but the screen was distorted and blurry, I never did figure out how to get it to work right. It looks great with the standard VGA cable, so I probably will leave it for now. I also have read that when you use the BNC connectors, you lose the DDC signal from the monitor the the video card. If I understand this correctly, it means that your monitor can no longer communicate it's ideal parameters for color/tint/brightness/etc... to the video card. In my startup screens before getting into Win98, it says 'DDC monitor detected, using optimal parameters supplied by your monitor' or something very close to that.
If you get yours working correctly with the BNC cables and do notice a difference, let me know!
When i got my first voodoo i had to use an BNC cable to make it work with my old IBM 9527 monitor. But the image was bad the higher the res. went. So i made my custom dsub cable without dcc. You only have to cut 2 pins on the conector
Works fine now.