Well , missed this topic completely.

You might look out for an adaptec 2940 model.
This is SCSI II but also works on all SCSI I devices. Is in fact downwards compatable.
You won't have the speed of SCSI II but only SCSI I.
The 2940 has it's own bios, which means you can set it up manually.

I use one for the connection between M Kurzweil 2600S and my PC.

What I don't know though do PCI cards fit in a Mac??? I don't own a Mac.

Then for your info;
The 2940 is 80 pins while my Kurzweil is 64 pins, which gives no problem at all with a 64 to 80 pin cable.

Hope this helps.

Fred