scsi.device in the 3.1 ROM doesn't handle ATAPI devices. I *think* the one from 3.9 does, so your CD0 should be looking for the CD drive as scsi.device, unit 1 (assuming your HD is set to master and the CD drive is slave). If the 3.9 ROM update isn't kicking in, or you're skipping the scsi.device update in the startup-sequence, this is a moot point since you'll then automatically fall back to the useless 3.1 version.
So then you'd need atapi.device from IDEFix, or asim_atapi.device from AsimCDFS.
EDIT: Can you post the output from version scsi.device?
