it is difficult question, I would recommend to call Yamaha hotline.
I only know, we had problems if we connected some devices over two SCSI adaptors:
device <-> SCSI adaptor <-> SCSI adaptor <-> SCSI device.
The first adaptor is in the PSR 9000, the second would be your SCSI card. If the PSR 9000 can communicate with SCSI adaptor (not directly SCSI device), then I would not see any other problems.
As I wrote, the best choice is to ask by the Yamaha hotline.