On the original ROM it's called oktagon.device I think.... if you use the later patched ROM (on the Aminet I think) then it's called 2nd.scsi.device I think, and also SoftSCSI_OktagonC9XEA.device or similar - the actual letters on the end change depending on where it is physically.
I used AsimCDFS but that should be all you need to know!