The Problem with SCSI-Networks is that there is no software for the Amiga to make it save (the Siamese package contained software that could do it, but is is nothing you would run on a plain A500).
Of course you could just put two SCSI controllers on the SCSI chain if you could jumper one of the controllers to another ID (usually controllers are hard wired to ID7 but some have jumpers for the own ID) but you have to make sure that there is no simultanious access to the same files as there is no software in place to handle blocking an releasing files during access from one or the other side.
Given the possible speed I alway wondered why there was no scsi networking software developed for the Amiga in the old day. Maybe because of the limitations of the cablelenght you could use.
