It would be much cheaper just to get a new USB or FireWire scanner. It would also be something you can use down the road if you ever have to get a new computer.

The only PCIe I can find for now is an ATTO EPCI-UL5D-L00. They run around $350 if you shop around. You would also need an adapter cable to go from the scanner to the different port on the card. So for what's looking like a $400 or so investment, you can buy a really nice FireWire or USB scanner.

The Umax has 1200x2400 optical resolution so keep that in mind when looking for a new one, optical resolution.

Your only other option is to try to find a SCSI to FireWire adapter that will actually work. Sorry but I don't have any recommendations for those. All of the ones I've seen are flaky, they work with some set ups but not with others.