Theres a typo
there though: "Matrox 400+500" is supposed to
be "Matrox 450+550". I'm afraid of those cards. They
made my machines behave strangely, hanging, lots of cpu use.
i had one of these in 2001, driving a dual setup. there were ghosts of the second screen
on the first. and oddly, it was a ghost of the VGA screen on the DVI screen (at the time,
the cards didnt have DVI, but they had this addon bridge thing which was unshielded pins
to another connector on a second pci slot). the bottom line is, the signal quality was
questionable, and the cards are massively obsolete.
are you sure this wasn't a cable issue? i've had similar problems caused
by using cheaper cabling that went away when i paid out for high end
cabling (my cable runs were long)