I really, REALLY doubt it has anything to do with the fact the card uses a PCI-bus. The fact that the speed of the card can be set to lower than 320 means that it IS designed to work with earlier SCSI devices. If the drives are recognised on the other machine, using the same cables & terminators, then I'm 99% sure it's a bad card. If it's new and you bought from a reputable dealer they should replace it.
Good luck, I'm off to bed...