Wow, I feel dumb now. I just got around to taking a second look at all of the connectors. What I hadn't seen earlier is that the scanner had a second input. So when I had the old 25 pin SCSI card in there, it was connected by a cable that went from the 25 pin card to the 50 pin connector on the scanner. But the second input on the scanner is 25 pin! So basically, I simply turned the cable around, 25 pin into the scanner and 50 pin into the tape drive, and I'm up and scanning after a reboot!!!

Just goes to show, kids. Look for the simple solutions first.