Optiplex 990 and 960 with NVIDIA NVS450 4 monitor support

We have several Optiplex 960 workstation with NVS450 video cards.  After the 960 was discontinued we tried to upgrade to the 990 but found that there was no 4 monitor solution so we tried using the NVS450 cards from the 960s.  After trying many different bios versions up to A13 we have concluded that the NVS450 will not work in the 990.  I was hoping someone else here may have a work around or may know of a 4 display port monitor solution for the Optiplex 990 workstations.